These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

Rotor Broadband Noise Prediction with Comparison to Model Data  

NASA Technical Reports Server (NTRS)

This paper reports an analysis and prediction development of rotor broadband noise. The two primary components of this noise are Blade-Wake Interaction (BWI) noise, due to the blades' interaction with the turbulent wakes of the preceding blades, and "Self" noise, due to the development and shedding of turbulence within the blades' boundary layers. Emphasized in this report is the new code development for Self noise. The analysis and validation employs data from the HART program, a model BO-105 rotor wind tunnel test conducted in the German-Dutch Wind Tunnel (DNW). The BWI noise predictions are based on measured pressure response coherence functions using cross-spectral methods. The Self noise predictions are based on previously reported semiempirical modeling of Self noise obtained from isolated airfoil sections and the use of CAMRAD.Modl to define rotor performance and local blade segment flow conditions. Both BWI and Self noise from individual blade segments are Doppler shifted and summed at the observer positions. Prediction comparisons with measurements show good agreement for a range of rotor operating conditions from climb to steep descent. The broadband noise predictions, along with those of harmonic and impulsive Blade-Vortex Interaction (BVI) noise predictions, demonstrate a significant advance in predictive capability for main rotor noise.

Brooks, Thomas F.; Burley, Casey L.

2001-01-01

2

Broadband Noise Predictions Based on a New Aeroacoustic Formulation  

NASA Technical Reports Server (NTRS)

A new analytic result in acoustics called 'Formulation 1B,' proposed by Farassat, is used to compute the loading noise from an unsteady surface pressure distribution on a thin airfoil in the time domain. This formulation is a new solution of the Ffowcs Williams-Hawkings equation with the loading source term. The formulation contains a far-field surface integral that depends on the time derivative and the surface gradient of the pressure on the airfoil, as well as a contour integral on the boundary of the airfoil surface. As a first test case, the new formulation is used to compute the noise radiated from a flat plate, moving through a sinusoidal gust of constant frequency. The unsteady surface pressure for this test case is specified analytically from a result that is based on linear airfoil theory. This test case is used to examine the velocity scaling properties of Formulation 1B, and to demonstrate its equivalence to Formulation 1A, of Farassat. The new acoustic formulation, again with an analytic surface pressure, is then used to predict broadband noise radiated from an airfoil immersed in homogeneous turbulence. The results are compared with experimental data previously reported by Paterson and Amiet. Good agreement between predictions and measurements is obtained. The predicted results also agree very well with those of Paterson and Amiet, who used a frequency-domain approach. Finally, an alternative form of Formulation 1B is described for statistical analysis of broadband noise.

Casper, J.; Farassat, F.

2002-01-01

3

A New Time Domain Formulation for Broadband Noise Predictions  

NASA Technical Reports Server (NTRS)

A new analytic result in acoustics called "Formulation 1B," proposed by Farassat, is used to compute the loading noise from an unsteady surface pressure distribution on a thin airfoil in the time domain. This formulation is a new solution of the Ffowcs Williams-Hawkings equation with the loading source term. The formulation contains a far field surface integral that depends on the time derivative and the surface gradient of the pressure on the airfoil, as well as a contour integral on the boundary of the airfoil surface. As a first test case, the new formulation is used to compute the noise radiated from a flat plate, moving through a sinusoidal gust of constant frequency. The unsteady surface pressure for this test case is analytically specified from a result based on linear airfoil theory. This test case is used to examine the velocity scaling properties of Formulation 1B and to demonstrate its equivalence to Formulation 1A of Farassat. The new acoustic formulation, again with an analytic surface pressure, is then used to predict broadband noise radiated from an airfoil immersed in homogeneous, isotropic turbulence. The results are compared with experimental data previously reported by Paterson and Amiet. Good agreement between predictions and measurements is obtained. Finally, an alternative form of Formulation 1B is described for statistical analysis of broadband noise.

Casper, J.; Farassat, F.

2002-01-01

4

A New Time Domain Formulation for Broadband Noise Predictions  

NASA Technical Reports Server (NTRS)

A new analytic result in acoustics called "Formulation 1B," proposed by Farassat, is used to compute the loading noise from an unsteady surface pressure distribution on a thin airfoil in the time domain. This formulation is a new solution of the Ffowcs Williams-Hawkings equation with the loading source term. The formulation contains a far field surface integral that depends on the time derivative and the surface gradient of the pressure on the airfoil, as well as a contour integral on the boundary of the airfoil surface. As a first test case, the new formulation is used to compute the noise radiated from a flat plate, moving through a sinusoidal gust of constant frequency. The unsteady surface pressure for this test case is analytically specied from a result based on linear airfoil theory. This test case is used to examine the velocity scaling properties of Formulation 1B and to demonstrate its equivalence to Formulation 1A of Farassat. The new acoustic formulation, again with an analytic surface pressure, is then used to predict broadband noise radiated from an airfoil immersed in homogeneous, isotropic turbulence. The results are compared with experimental data previously reported by Paterson and Amiet. Good agreement between predictions and measurements is obtained. Finally, an alternative form of Formulation 1B is described for statistical analysis of broadband noise.

Casper, Jay H.; Farassat, Fereidoun

2002-01-01

5

The prediction of broadband shock-associated noise using Reynolds-averaged Navier-Stokes solutions  

Microsoft Academic Search

Broadband shock-associated noise is a component of jet noise generated by supersonic jets operating off-design. It is characterized by multiple broadband peaks and dominates the total noise at large angles to the jet downstream axis. A new model is introduced for the prediction of broadband shock-associated noise that uses the solution of the Reynolds averaged Navier-Stokes equations. The noise model

Steven Arthur Eric Miller

2009-01-01

6

The Prediction of Broadband Shock-Associated Noise from Dualstream and Rectangular Jets Using RANS CFD  

NASA Technical Reports Server (NTRS)

Supersonic jets operating off-design produce broadband shock-associated noise. Broadband shock-associated noise is characterized by multiple broadband peaks in the far-field and is often the dominant source of noise towards the sideline and upstream direction relative to the jet axis. It is due to large scale coherent turbulence structures in the jet shear layers interacting with the shock cell structure. A broadband shock-associated noise model recently developed by the authors predicts this noise component from solutions to the Reynolds averaged Navier-Stokes equations using a two-equation turbulence model. The broadband shock-associated noise model is applied to dualstream and rectangular nozzles operating supersonically, heated, and off-design. The dualstream jet broadband shock-associated noise predictions are conducted for cases when the core jet is supersonic and the fan jet is subsonic, the core jet is subsonic and the fan jet is supersonic, and when both jet streams operate supersonically. Rectangular jet predictions are shown for a convergent-divergent nozzle operating both over- and under-expanded for cold and heated conditions. The original model implementation has been heavily modified to make accurate predictions for the dualstream jets. It is also argued that for over-expanded jets the oblique shock wave attached to the nozzle lip contributes little to broadband shock-associated noise. All predictions are compared with experiments.

Miller, Steven A.; Morris, Philip J.

2010-01-01

7

The prediction of broadband shock-associated noise using Reynolds-averaged Navier-Stokes solutions  

NASA Astrophysics Data System (ADS)

Broadband shock-associated noise is a component of jet noise generated by supersonic jets operating off-design. It is characterized by multiple broadband peaks and dominates the total noise at large angles to the jet downstream axis. A new model is introduced for the prediction of broadband shock-associated noise that uses the solution of the Reynolds averaged Navier-Stokes equations. The noise model is an acoustic analogy based on the linearized Euler equations. The equivalent source terms depend on the product of the fluctuations associated with the shock cell structure and the turbulent velocity fluctuations in the jet shear layer. The former are deterministic and are obtained from the Reynolds averaged Navier-Stokes solution. A statistical model is introduced to describe the properties of the turbulence. Only the geometry and operating conditions of the nozzle need to be known to make noise predictions. Unlike other models, the developed broadband shock-associated noise model is a true prediction scheme and not calibrated for a finite range of operating conditions. The broadband shock-associated noise model developed represents the only prediction method in existence that has no restrictions on nozzle geometry or jet operating conditions. This overcomes the limitations and empiricism present in previous broadband shock-associated noise models. Extensive validation of the Reynolds averaged Navier-Stokes solution is performed using experimental data. Validation efforts of the Reynolds averaged Navier-Stokes solutions include comparisons of Pitot and static probe measurements and schlieren visualization. These validations show both the strengths and deficiencies for modeling strategies of supersonic jets operating off-design using Reynolds averaged Navier-Stokes equations and associated turbulence closure schemes. Predictions for various nozzle and operating conditions are compared with experimental noise measurements of the associated jets to validate the broadband shock-associated noise model. The operating conditions include under-expanded and over-expanded jets with and without heating.

Miller, Steven Arthur Eric

8

Broadband Noise Predictions for an Airfoil in a Turbulent Stream  

NASA Technical Reports Server (NTRS)

Loading noise is predicted from unsteady surface pressure measurements on a NACA 0015 airfoil immersed in grid-generated turbulence. The time-dependent pressure is obtained from an array of synchronized transducers on the airfoil surface. Far field noise is predicted by using the time-dependent surface pressure as input to Formulation 1A of Farassat, a solution of the Ffowcs Williams - Hawkings equation. Acoustic predictions are performed with and without the effects of airfoil surface curvature. Scaling rules are developed to compare the present far field predictions with acoustic measurements that are available in the literature.

Casper, J.; Farassat, F.; Mish, P. F.; Devenport, W. J.

2003-01-01

9

Prediction of broadband noise from large horizontal axis wind turbine generators  

NASA Technical Reports Server (NTRS)

A method is presented for predicting the broadband noise spectra of large horizontal axis wind turbine generators. It includes contributions from such noise sources as the inflow turbulence to the rotor, the interactions between the turbulent boundary layers on the blade surfaces with their trailing edges and the wake due to a blunt trailing edge. The method is partly empirical and is based on acoustic measurements of large wind turbines and airfoil models. The predicted frequency spectra are compared with measured data from several machines including the MOD-OA, the MOD-2, the WTS-4 and the U.S. Wind-power Inc. machine. Also included is a broadband noise prediction for the proposed MOD-5B. The significance of the effects of machine size, power output, trailing edge bluntness and distance to the receiver is illustrated. Good agreement is obtained between the predicted and measured far field noise spectra.

Grosveld, F. W.

1984-01-01

10

Broadband Fan Noise Prediction System for Turbofan Engines. Volume 3; Validation and Test Cases  

NASA Technical Reports Server (NTRS)

Pratt & Whitney has developed a Broadband Fan Noise Prediction System (BFaNS) for turbofan engines. This system computes the noise generated by turbulence impinging on the leading edges of the fan and fan exit guide vane, and noise generated by boundary-layer turbulence passing over the fan trailing edge. BFaNS has been validated on three fan rigs that were tested during the NASA Advanced Subsonic Technology Program (AST). The predicted noise spectra agreed well with measured data. The predicted effects of fan speed, vane count, and vane sweep also agreed well with measurements. The noise prediction system consists of two computer programs: Setup_BFaNS and BFaNS. Setup_BFaNS converts user-specified geometry and flow-field information into a BFaNS input file. From this input file, BFaNS computes the inlet and aft broadband sound power spectra generated by the fan and FEGV. The output file from BFaNS contains the inlet, aft and total sound power spectra from each noise source. This report is the third volume of a three-volume set documenting the Broadband Fan Noise Prediction System: Volume 1: Setup_BFaNS User s Manual and Developer s Guide; Volume 2: BFaNS User s Manual and Developer s Guide; and Volume 3: Validation and Test Cases. The present volume begins with an overview of the Broadband Fan Noise Prediction System, followed by validation studies that were done on three fan rigs. It concludes with recommended improvements and additional studies for BFaNS.

Morin, Bruce L.

2010-01-01

11

A prediction method for broadband shock associated noise from supersonic rectangualr jets  

NASA Technical Reports Server (NTRS)

Braodband shock associated noise is an important aircraft noise component of the proposed high-speed civil transport (HSCT) at take-offs and landings. For noise certification purpose one would, therefore, like to be able to predict as accurately as possible the intensity, directivity and spectral content of this noise component. The purpose of this work is to develop a semi-empirical prediction method for the broadband shock associated noise from supersonic rectangular jets. The complexity and quality of the noise prediction method are to be similar to those for circular jets. In this paper only the broadband shock associated noise of jets issued from rectangular nozzles with straight side walls is considered. Since many current aircraft propulsion systems have nozzle aspect ratios (at nozzle exit) in the range of 1 to 4, the present study has been confined to nozzles with aspect ratio less than 6. In developing the prediction method the essential physics of the problem are taken into consideration. Since the braodband shock associated noise generation mechanism is the same whether the jet is circular or round the present prediction method in a number of ways is quite similar to that for axisymmetric jets. Comparisons between predictions and measurements for jets with aspect ratio up to 6 will be reported. Efforts will be concentrated on the fly-over plane. However, side line angles and other directions will also be included.

Tam, Christopher K. W.; Reddy, N. N.

1993-01-01

12

A frequency domain numerical method for airfoil broadband self-noise prediction  

NASA Astrophysics Data System (ADS)

This paper describes a numerical approach, based in the frequency domain, for predicting the broadband self-noise radiation due to an airfoil situated in a smooth mean flow. Noise is generated by the interaction between the boundary layer turbulence on the airfoil surface and the airfoil trailing edge. Thin airfoil theory is used to deduce the unsteady blade loading. In this paper, the important difference with much of the previous work dealing with trailing edge noise is that the integration of the surface sources for computation of the radiated sound field is evaluated on the actual airfoil surface rather than in the mean-chord plane. The assumption of flat plate geometry in the calculation of radiation is therefore avoided. Moreover, the solution is valid in both near and far fields and reduces to the analytic solution due to Amiet when the airfoil collapses to a flat plate with large span, and the measurement point is taken to the far field. Predictions of the airfoil broadband self-noise radiation presented here are shown to be in reasonable agreement with the predictions obtained using the Brooks approach, which are based on a comprehensive database of experimental data. Also investigated in this paper is the effect on the broadband noise prediction of relaxing the 'frozen-gust' assumption, whereby the turbulence at each frequency comprises a continuous spectrum of streamwise wavenumber components. It is shown that making the frozen gust assumption yields an under-prediction of the noise spectrum by approximately 2dB compared with that obtained when this assumption is relaxed, with the largest occurring at high frequencies. This paper concludes with a comparison of the broadband noise directivity for a flat-plat, a NACA 0012 and a NACA 0024 airfoil at non-zero angle of attack. Differences of up to 20 dB are predicted, with the largest difference occurring at a radiation angle of zero degrees relative to the airfoil mean centre line.

Zhou, Qidou; Joseph, Phillip

2007-01-01

13

Broadband noise prediction of fan outlet guide vane using a cascade response function  

Microsoft Academic Search

An analytical model of the broadband noise produced by both the interaction of ingested turbulence with a fan rotor blades and the rotor-wake impingement on downstream stator vanes is proposed and detailed. The noise prediction methodology is a strip-theory approach based on a previously published formulation of the three-dimensional unsteady blade loading for a rectilinear cascade. This three-dimensional cascade response

H. Posson; S. Moreau; M. Roger

2011-01-01

14

Measurement and prediction of broadband noise from large horizontal axis wind turbine generators  

NASA Technical Reports Server (NTRS)

A method is presented for predicting the broadband noise spectra of large wind turbine generators. It includes contributions from such noise sources as the inflow turbulence to the rotor, the interactions between the turbulent boundary layers on the blade surfaces with their trailing edges and the wake due to a blunt trailing edge. The method is partly empirical and is based on acoustic measurements of large wind turbines and airfoil models. Spectra are predicted for several large machines including the proposed MOD-5B. Measured data are presented for the MOD-2, the WTS-4, the MOD-OA, and the U.S. Windpower Inc. machines. Good agreement is shown between the predicted and measured far field noise spectra.

Grosveld, F. W.; Shepherd, K. P.; Hubbard, H. H.

1995-01-01

15

Stochastic prediction of broadband shock-associated noise including propagation effects  

E-print Network

at off-design conditions, supersonic jets produce BroadBand Shock-Associated Noise (BBSAN). The noise. BBSAN radiation is characterized by multiple frequency humps dominating the jet mixing noise jet flow exiting from the aft of the secondary nozzle and producing supersonic jet noise. Supersonic

Paris-Sud XI, Université de

16

Prediction of Broadband Shock-Associated Noise Including Propagation Effects Originating NASA  

NASA Technical Reports Server (NTRS)

An acoustic analogy is developed based on the Euler equations for broadband shock-associated noise (BBSAN) that directly incorporates the vector Green s function of the linearized Euler equations and a steady Reynolds-Averaged Navier-Stokes solution (SRANS) to describe the mean flow. The vector Green s function allows the BBSAN propagation through the jet shear layer to be determined. The large-scale coherent turbulence is modeled by two-point second order velocity cross-correlations. Turbulent length and time scales are related to the turbulent kinetic energy and dissipation rate. An adjoint vector Green s function solver is implemented to determine the vector Green s function based on a locally parallel mean flow at different streamwise locations. The newly developed acoustic analogy can be simplified to one that uses the Green s function associated with the Helmholtz equation, which is consistent with a previous formulation by the authors. A large number of predictions are generated using three different nozzles over a wide range of fully-expanded jet Mach numbers and jet stagnation temperatures. These predictions are compared with experimental data from multiple jet noise experimental facilities. In addition, two models for the so-called fine-scale mixing noise are included in the comparisons. Improved BBSAN predictions are obtained relative to other models that do not include propagation effects.

Miller, Steven; Morris, Philip J.

2012-01-01

17

Broadband Fan Noise Prediction System for Turbofan Engines. Volume 2; BFaNS User's Manual and Developer's Guide  

NASA Technical Reports Server (NTRS)

Pratt & Whitney has developed a Broadband Fan Noise Prediction System (BFaNS) for turbofan engines. This system computes the noise generated by turbulence impinging on the leading edges of the fan and fan exit guide vane, and noise generated by boundary-layer turbulence passing over the fan trailing edge. BFaNS has been validated on three fan rigs that were tested during the NASA Advanced Subsonic Technology Program (AST). The predicted noise spectra agreed well with measured data. The predicted effects of fan speed, vane count, and vane sweep also agreed well with measurements. The noise prediction system consists of two computer programs: Setup_BFaNS and BFaNS. Setup_BFaNS converts user-specified geometry and flow-field information into a BFaNS input file. From this input file, BFaNS computes the inlet and aft broadband sound power spectra generated by the fan and FEGV. The output file from BFaNS contains the inlet, aft and total sound power spectra from each noise source. This report is the second volume of a three-volume set documenting the Broadband Fan Noise Prediction System: Volume 1: Setup_BFaNS User s Manual and Developer s Guide; Volume 2: BFaNS User s Manual and Developer s Guide; and Volume 3: Validation and Test Cases. The present volume begins with an overview of the Broadband Fan Noise Prediction System, followed by step-by-step instructions for installing and running BFaNS. It concludes with technical documentation of the BFaNS computer program.

Morin, Bruce L.

2010-01-01

18

Broadband Fan Noise Prediction System for Turbofan Engines. Volume 1; Setup_BFaNS User's Manual and Developer's Guide  

NASA Technical Reports Server (NTRS)

Pratt & Whitney has developed a Broadband Fan Noise Prediction System (BFaNS) for turbofan engines. This system computes the noise generated by turbulence impinging on the leading edges of the fan and fan exit guide vane, and noise generated by boundary-layer turbulence passing over the fan trailing edge. BFaNS has been validated on three fan rigs that were tested during the NASA Advanced Subsonic Technology Program (AST). The predicted noise spectra agreed well with measured data. The predicted effects of fan speed, vane count, and vane sweep also agreed well with measurements. The noise prediction system consists of two computer programs: Setup_BFaNS and BFaNS. Setup_BFaNS converts user-specified geometry and flow-field information into a BFaNS input file. From this input file, BFaNS computes the inlet and aft broadband sound power spectra generated by the fan and FEGV. The output file from BFaNS contains the inlet, aft and total sound power spectra from each noise source. This report is the first volume of a three-volume set documenting the Broadband Fan Noise Prediction System: Volume 1: Setup_BFaNS User s Manual and Developer s Guide; Volume 2: BFaNS User's Manual and Developer s Guide; and Volume 3: Validation and Test Cases. The present volume begins with an overview of the Broadband Fan Noise Prediction System, followed by step-by-step instructions for installing and running Setup_BFaNS. It concludes with technical documentation of the Setup_BFaNS computer program.

Morin, Bruce L.

2010-01-01

19

UHB engine fan broadband noise reduction study  

Microsoft Academic Search

A study has been completed to quantify the contribution of fan broadband noise to advanced high bypass turbofan engine system noise levels. The result suggests that reducing fan broadband noise can produce 3 to 4 EPNdB in engine system noise reduction, once the fan tones are eliminated. Further, in conjunction with the elimination of fan tones and an increase in

Philip R. Gliebe; Patrick Y. Ho; Ramani Mani

1995-01-01

20

CFD Computation of Broadband Fan Interaction Noise  

NASA Technical Reports Server (NTRS)

In this study, a 3-D, unsteady, Reynolds Averaged Navier Stokes CFD code coupled to an acoustic calculation is used to predict the contribution of the exit guide vanes to broadband fan noise. The configuration investigated is that corresponding to the NASA Source Diagnostic Test (SDT) 22-in fan rig. Then an acoustic model introduced by Nallasamy which is based on 2-D strip theory is used to compute the broadband rotor-stator interaction noise. One configuration from the SDT matrix is considered here: the fan speed correlating to approach, and outlet guide vane count designed for cut-off of the blade passage frequency. Thus, in the chosen configuration, there are 22 rotor blades and 54 stator blades. The stators are located 2.5 tip chords downstream of the rotor trailing edge. The RANS computations are used to obtain the spectra of the unsteady surface pressure on the exit guide vanes. This surface pressure is then integrated together with the Green's function for and infinite cylindrical duct to obtain the acoustic field. The results from this investigation validate the use of the CFD code along with the acoustic model for broadband fan noise predictions. The validation enables future investigations such as the determination of rotor tip clearance and stator solidity effects on fan rotor-stator interaction noise.

Grace, Sheryl M.; Sondak, Douglas L.; Dorney, Daniel J.

2007-01-01

21

Predicting Noise From Wind Turbines  

NASA Technical Reports Server (NTRS)

Computer program WINDY predicts broadband noise spectra of horizontal-axis wind-turbine generators. Enables adequate assessment of impact of broadband wind-turbine noise. Effects of turbulence, trailing-edge wakes, and bluntness taken into account. Program has practical application in design and siting of wind-turbine machines acceptable to community. Written in GW-Basic.

Grosveld, Ferdinand W.

1990-01-01

22

Predicting broadband noise from a stator vane of a gas turbine engine  

NASA Technical Reports Server (NTRS)

A computer-implemented model of fan section of a gas turbine engine accounts for the turbulence in the gas flow emanating from the rotor assembly and impinging upon an inlet to the stator vane cascade. The model allows for user-input variations in the sweep and/or lean angles for the stator vanes. The model determines the resulting acoustic response of the fan section as a function of the turbulence and the lean and/or sweep angles of the vanes. The model may be embodied in software that is rapidly executed in a computer. This way, an optimum arrangement in terms of fan noise reduction is quickly determined for the stator vane lean and sweep physical positioning in the fan section of a gas turbine engine.

Hanson, Donald B. (Inventor)

2002-01-01

23

UHB Engine Fan Broadband Noise Reduction Study  

NASA Technical Reports Server (NTRS)

A study has been completed to quantify the contribution of fan broadband noise to advanced high bypass turbofan engine system noise levels. The result suggests that reducing fan broadband noise can produce 3 to 4 EPNdB in engine system noise reduction, once the fan tones are eliminated. Further, in conjunction with the elimination of fan tones and an increase in bypass ratio, a potential reduction of 7 to 10 EPNdB in system noise can be achieved. In addition, an initial assessment of engine broadband noise source mechanisms has been made, concluding that the dominant source of fan broadband noise is the interaction of incident inlet boundary layer turbulence with the fan rotor. This source has two contributors, i.e., unsteady life dipole response and steady loading quadrupole response. The quadrupole contribution was found to be the most important component, suggesting that broadband noise reduction can be achieved by the reduction of steady loading field-turbulence field quadrupole interaction. Finally, for a controlled experimental quantification and verification, the study recommends that further broadband noise tests be done on a simulated engine rig, such as the GE Aircraft Engine Universal Propulsion Simulator, rather than testing on an engine statically in an outdoor arena The rig should be capable of generating forward and aft propagating fan noise, and it needs to be tested in a large freejet or a wind tunnel.

Gliebe, Philip R.; Ho, Patrick Y.; Mani, Ramani

1995-01-01

24

Discrete-frequency and broadband noise radiation from diesel engine cooling fans  

Microsoft Academic Search

This effort focuses on measuring and predicting the discrete-frequency and broadband noise radiated by diesel engine cooling fans. Unsteady forces developed by the interaction of the fan blade with inlet flow are the dominant source for both discrete-frequency and broadband noise of the subject propeller fan. In many cases, a primary source of discrepancy between fan noise prediction and measurement

Geon-Seok Kim

2007-01-01

25

Main rotor broadband noise study in the DNW  

NASA Technical Reports Server (NTRS)

An acoustics test of a 2/5 scale model BO-105 helicopter main rotor was conducted in the Duits-Nederlandse Windtunnel (DNW). A range of operating conditions was tested from hover to moderately high flight speeds for various climb and descent rates at different thrust settings. Diagnostic tests including rotor speed and blade geometry changes were made to better isolate and study particular broadband self noise sources. Acoustic data in the form of acoustic pressure time histories and power spectra are used to demonstrate the regions of importance of the different broadband noise sources and their sensitivity to operating conditions. To help interpret the data, comparisons are made to predictions of rotor broadband noise. The predictions are based on self noise data previously obtained from isolated airfoil sections and the use of the NASA ROTONET program to define rotor performance and to sum contributions of noise from individual blade segments. An important result herein is the identification and articulation of a previously unheralded rotor broadband noise source. This source is blade-turbulent wake interaction (BWI) noise which dominates the spectra in the mid-frequencies for off-peak blade-vortex interaction (BVI) noise flight conditions.

Brooks, Thomas F.; Marcolini, Michael A.; Pope, D. Stuart

1987-01-01

26

Broadband Shock Noise Reduction in Turbulent Jets by Water Injection  

NASA Technical Reports Server (NTRS)

The concept of effective jet properties introduced by the author (AIAA-2007-3 645) has been extended to the estimation of broadband shock noise reduction by water injection in supersonic jets. Comparison of the predictions with the test data for cold underexpanded supersonic nozzles shows a satisfactory agreement. The results also reveal the range of water mass flow rates over which saturation of mixing noise reduction and existence of parasitic noise are manifest.

Kandula, Max

2008-01-01

27

Aircraft noise prediction program theoretical manual: Rotorcraft System Noise Prediction System (ROTONET), part 4  

NASA Technical Reports Server (NTRS)

This document describes the theoretical methods used in the rotorcraft noise prediction system (ROTONET), which is a part of the NASA Aircraft Noise Prediction Program (ANOPP). The ANOPP code consists of an executive, database manager, and prediction modules for jet engine, propeller, and rotor noise. The ROTONET subsystem contains modules for the prediction of rotor airloads and performance with momentum theory and prescribed wake aerodynamics, rotor tone noise with compact chordwise and full-surface solutions to the Ffowcs-Williams-Hawkings equations, semiempirical airfoil broadband noise, and turbulence ingestion broadband noise. Flight dynamics, atmosphere propagation, and noise metric calculations are covered in NASA TM-83199, Parts 1, 2, and 3.

Weir, Donald S.; Jumper, Stephen J.; Burley, Casey L.; Golub, Robert A.

1995-01-01

28

Prediction of airframe noise  

NASA Technical Reports Server (NTRS)

Methods of predicting airframe noise generated by aircraft in flight under nonpowered conditions are discussed. Approaches to predictions relying on flyover data and component theoretical analyses are developed. A nondimensional airframe noise spectrum of various aircraft is presented. The spectrum was obtained by smoothing all the measured spectra to remove any peculiarities due to airframe protrusions, normalizing each spectra by its overall sound pressure level and a characteristics frequency, and averaging the spectra together. A chart of airframe noise sources is included.

Hardin, J. C.; Fratello, D. J.; Hayden, R. E.; Kadman, Y.; Africk, S.

1975-01-01

29

Fan Noise Prediction  

NASA Technical Reports Server (NTRS)

Aircraft noise emission level restrictions in and around airports continue to grow more stringent every few years. Thus, it is important to predict noise emissions from aircraft accurately. Predicting noise from the engine(s) is an integral part of the efforts to characterize the noise signature of an aircraft. An important source of engine noise is the rotor-stator interaction noise produced as a result of impingement of fan rotor wakes on the fan exit guide vanes. Interaction noise propagates through the inlet and exhaust ducts of the engine and radiates to the far field. noise levels for a range of model fans stages that represent current aircraft engine designs. Eversman's radiation codes calculate both the inlet and exhaust noise radiation by propagating the internally measured rotor-stator interaction noise to the far field. Predicted far field sound pressure levels are then compared to the measured levels from wind tunnel tests. This effort's objective is to prove that the predicted levels actually describe the measured levels.

France, Joshua I.

2004-01-01

30

Airfoil self-noise and prediction  

NASA Technical Reports Server (NTRS)

A prediction method is developed for the self-generated noise of an airfoil blade encountering smooth flow. The prediction methods for the individual self-noise mechanisms are semiempirical and are based on previous theoretical studies and data obtained from tests of two- and three-dimensional airfoil blade sections. The self-noise mechanisms are due to specific boundary-layer phenomena, that is, the boundary-layer turbulence passing the trailing edge, separated-boundary-layer and stalled flow over an airfoil, vortex shedding due to laminar boundary layer instabilities, vortex shedding from blunt trailing edges, and the turbulent vortex flow existing near the tip of lifting blades. The predictions are compared successfully with published data from three self-noise studies of different airfoil shapes. An application of the prediction method is reported for a large scale-model helicopter rotor, and the predictions compared well with experimental broadband noise measurements. A computer code of the method is given.

Brooks, Thomas F.; Pope, D. Stuart; Marcolini, Michael A.

1989-01-01

31

Airfoil self-noise and prediction  

NASA Astrophysics Data System (ADS)

A prediction method is developed for the self-generated noise of an airfoil blade encountering smooth flow. The prediction methods for the individual self-noise mechanisms are semiempirical and are based on previous theoretical studies and data obtained from tests of two- and three-dimensional airfoil blade sections. The self-noise mechanisms are due to specific boundary-layer phenomena, that is, the boundary-layer turbulence passing the trailing edge, separated-boundary-layer and stalled flow over an airfoil, vortex shedding due to laminar boundary layer instabilities, vortex shedding from blunt trailing edges, and the turbulent vortex flow existing near the tip of lifting blades. The predictions are compared successfully with published data from three self-noise studies of different airfoil shapes. An application of the prediction method is reported for a large scale-model helicopter rotor, and the predictions compared well with experimental broadband noise measurements. A computer code of the method is given.

Brooks, Thomas F.; Pope, D. Stuart; Marcolini, Michael A.

1989-07-01

32

Estimation of Broadband Shock Noise Reduction in Turbulent Jets by Water Injection  

NASA Technical Reports Server (NTRS)

The concept of effective jet properties introduced by the authors (AIAA-2007-3645) has been extended to the estimation of broadband shock noise reduction by water injection in supersonic jets. Comparison of the predictions with the test data for cold underexpanded supersonic nozzles shows a satisfactory agreement. The results also reveal the range of water mass flow rates over which saturation of mixing noise reduction and existence of parasitic noise are manifest.

Kandula, Max; Lonerjan, Michael J.

2008-01-01

33

Direct Observation of Broadband Coating Thermal Noise in a Suspended Interferometer  

E-print Network

We have directly observed broadband thermal noise in silica/tantala coatings in a high-sensitivity Fabry-Perot interferometer. Our result agrees well with the prediction based on indirect, ring-down measurements of coating mechanical loss, validating that method as a tool for the development of advanced interferometric gravitational-wave detectors.

Eric D. Black; Akira Villar; Kyle Barbary; Adam Bushmaker; Jay Heefner; Seiji Kawamura; Fumiko Kawazoe; Luca Matone; Sharon Meidt; Shanti R. Rao; Kevin Schulz; Michael Zhang; Kenneth G. Libbrecht

2004-01-09

34

JET Noise Prediction  

NASA Technical Reports Server (NTRS)

Aerodynamic noise prediction has been an important and challenging research area since James Lighthill first introduced his Acoustic Analogy Approach over fifty years ago. This talk attempts to provide a unified framework for the subsequent theoretical developments in this field. It assumes that there is no single approach that is optimal in all situations and uses the framework as a basis for discussing the strengths weaknesses of the various approaches to this topic. But the emphasis here will be on the important problem of predicting the noise from high speed air jets. Specific results will presented for round jets in the 0.5 to 1.4 Mach number range and compared with experimental data taken on the Glenn SHAR rig. It is demonstrated that non-parallel mean flow effects play an important role in predicting the noise at the supersonic Mach numbers. The results explain the failure of previous attempts based on the parallel flow Lilley model (which has served as the foundation for most jet noise analyses during past two decades).

Goldstein, M. E.; Leib, S. J.

2007-01-01

35

Suppression of Spin Projection Noise in Broadband Atomic Magnetometry  

SciTech Connect

We demonstrate that quantum nondemolition measurement, combined with a suitable parameter estimation procedure, can improve the sensitivity of a broadband atomic magnetometer by reducing uncertainty due to spin projection noise. Furthermore, we provide evidence that real-time quantum feedback control offers robustness to classical uncertainties, including shot-to-shot atom number fluctuations, that would otherwise prevent quantum-limited performance.

Geremia, J.M.; Stockton, John K.; Mabuchi, Hideo [Physics and Control and Dynamical Systems, California Institute of Technology, Pasadena California 91125 (United States)

2005-05-27

36

Fan noise prediction assessment  

NASA Technical Reports Server (NTRS)

This report is an evaluation of two techniques for predicting the fan noise radiation from engine nacelles. The first is a relatively computational intensive finite element technique. The code is named ARC, an abbreviation of Acoustic Radiation Code, and was developed by Eversman. This is actually a suite of software that first generates a grid around the nacelle, then solves for the potential flowfield, and finally solves the acoustic radiation problem. The second approach is an analytical technique requiring minimal computational effort. This is termed the cutoff ratio technique and was developed by Rice. Details of the duct geometry, such as the hub-to-tip ratio and Mach number of the flow in the duct, and modal content of the duct noise are required for proper prediction.

Bent, Paul H.

1995-01-01

37

Sources, control, and effects of noise from aircraft propellers and rotors. [noise prediction (aircraft  

NASA Technical Reports Server (NTRS)

Source noise predictions are compared with measurements for conventional low-speed propellers, for new high speed propellers (propfans), and for a helicopter. Results from a light aircraft demonstration program are described, indicating that about 5-dB reduction of flyover noise can be obtained without significant performance penalty. Sidewall design studies are described for interior noise control in light general aviation aircraft and in large transports using propfan propulsion. The weight of the added acoustic treatment is estimated and tradeoffs between weight and noise reduction are discussed. A laboratory study of passenger response to combined broadband and tonal propeller like noise is described. Subject discomfort ratings of combined tone broadband noises are compared with ratings of broadband (boundary layer) noise alone, and the relative importance of the propeller tones is examined.

Mixson, J. S.; Greene, G. C.; Dempsey, T. K.

1981-01-01

38

Helicopter rotor trailing edge noise. [noise prediction  

NASA Technical Reports Server (NTRS)

A two dimensional section of a helicopter main rotor blade was tested in an acoustic wind tunnel at close to full-scale Reynolds numbers to obtain boundary layer data and acoustic data for use in developing an acoustic scaling law and testing a first principles trailing edge noise theory. Results were extended to the rotating frame coordinate system to develop a helicopter rotor trailing edge noise prediction. Comparisons of the calculated noise levels with helicopter flyover spectra demonstrate that trailing edge noise contributes significantly to the total helicopter noise spectrum at high frequencies. This noise mechanism is expected to control the minimum rotor noise. In the case of noise radiation from a local blade segment, the acoustic directivity pattern is predicted by the first principles trailing edge noise theory. Acoustic spectra are predicted by a scaling law which includes Mach number, boundary layer thickness and observer position. Spectrum shape and sound pressure level are also predicted by the first principles theory but the analysis does not predict the Strouhal value identifying the spectrum peak.

Schlinker, R. H.; Amier, R. K.

1981-01-01

39

Boeing 18-Inch Fan Rig Broadband Noise Test  

NASA Technical Reports Server (NTRS)

The purposes of the subject test were to identify and quantify the mechanisms by which fan broadband noise is produced, and to assess the validity of such theoretical models of those mechanisms as may be available. The test was conducted with the Boeing 18-inch fan rig in the Boeing Low-Speed Aeroacoustic Facility (LSAF). The rig was designed to be particularly clean and geometrically simple to facilitate theoretical modeling and to minimize sources of interfering noise. The inlet is cylindrical and is equipped with a boundary layer suction system. The fan is typical of modern high-by-pass ratio designs but is capable of operating with or without fan exit guide vanes (stators), and there is only a single flow stream. Fan loading and tip clearance are adjustable. Instrumentation included measurements of fan performance, the unsteady flow field incident on the fan and stators, and far-field and in-duct acoustic fields. The acoustic results were manipulated to estimate the noise generated by different sources. Significant fan broadband noise was found to come from the rotor self-noise as measured with clean inflow and no boundary layer. The rotor tip clearance affected rotor self-noise somewhat. The interaction of the rotor with inlet boundary layer turbulence is also a significant source, and is strongly affected by rotor tip clearance. High level noise can be generated by a high-order nonuniform rotating at a fraction of the fan speed, at least when tip clearance and loading are both large. Stator-generated noise is the loudest of the significant sources, by a small margin, at least on this rig. Stator noise is significantly affected by propagation through the fan.

Ganz, Ulrich W.; Joppa, Paul D.; Patten, Timothy J.; Scharpf, Daniel F.

1998-01-01

40

Trailing Edge Noise Prediction Based on a New Acoustic Formulation  

NASA Technical Reports Server (NTRS)

A new analytic result in acoustics called 'Formulation 1B,' proposed by Farassat, is used to compute broadband trailing edge noise from an unsteady surface pressure distribution on a thin airfoil in the time domain. This formulation is a new solution of the Ffowcs Williams-Hawkings equation with the loading source term, and has been shown in previous research to provide time domain predictions of broadband noise that are in excellent agreement with experiment. Furthermore, this formulation lends itself readily to rotating reference frames and statistical analysis of broadband trailing edge noise. Formulation 1B is used to calculate the far field noise radiated from the trailing edge of a NACA 0012 airfoil in low Mach number flows, using both analytical and experimental data on the airfoil surface. The results are compared to analytical results and experimental measurements that are available in the literature. Good agreement between predictions and measurements is obtained.

Casper, J.; Farassat, F.

2002-01-01

41

Overview of Aircraft Noise Prediction Tools Assessment  

NASA Technical Reports Server (NTRS)

The acoustic assessment task for both the Subsonic Fixed Wing and the Supersonic projects under NASA s Fundamental Aeronautics Program was designed to assess the current state-of-the-art in noise prediction capability and to establish baselines for gauging future progress. The documentation of our current capabilities included quantifying the differences between predictions of noise from computer codes and measurements of noise from experimental tests. Quantifying the accuracy of both the computed and experimental results further enhanced the credibility of the assessment. This presentation gives sample results from codes representative of NASA s capabilities in aircraft noise prediction at the system level and at the component level. These include semi-empirical, statistical, analytical, and numerical codes. An example of system level results is shown for an aircraft. Component level results are shown for airframe flaps and landing gear, for jet noise from a variety of nozzles, and for broadband fan noise. Additional results are shown for modeling of the acoustic behavior of duct acoustic lining and the attenuation of sound in lined ducts with flow.

Dahl, Milo D.

2007-01-01

42

Upper displacement limits for spatially broadband patterns containing bandpass noise.  

PubMed

How is the spatial-frequency content of a moving broadband pattern analysed by the visual system? Observers were asked to discriminate the direction of motion in random-noise patterns containing equal energy in each two-dimensional octave band. Uncorrelated noise could be introduced into either low- or high-frequency bands in order to force the visual system to rely on the outputs of putative mechanisms tuned to a narrow frequency range of the stimulus. In two experiments the dependent measure was the magnitude of dmax, the largest discrete displacement whose direction could be discriminated reliably. It was found that dmax was unaffected by the presence of high-frequency noise reaching down to 0.67 c/deg, but that the task became impossible thereafter. In the case of low-frequency noise, dmax fell as the noise was moved up towards about 2 c/deg, at which point the task became impossible at any displacement. This pattern of results would be expected if the system were using information from the lowest signal frequencies in all conditions. In experiment 2, dmax was measured for stimuli in which the spectral position and quantity of high-frequency noise were manipulated. It was found that only noise spectrally-adjacent to the signal band has a detrimental effect on dmax. Three different single-filter models of motion detection each failed to provide a satisfactory account of the spatial-frequency range of good direction discrimination performance. Rather, the modelling shows that the visual system can access the outputs of a low-frequency channel when the noise is high and a high-frequency channel when the noise is low. PMID:9797956

Eagle, R A

1998-06-01

43

Transonic Tones and Excess Broadband Noise in Overexpanded Supersonic Jets  

NASA Technical Reports Server (NTRS)

Noise characteristics of convergent-divergent (C-D) nozzles in the overexpanded regime are the focus of this paper. The flow regime is encountered during takeoff and landing of certain airplanes and also with rocket nozzles in launch-pad environment. Experimental results from laboratory-scale single nozzles are discussed. The flow often undergoes a resonance accompanied by emission of tones (referred to as transonic tones). The phenomenon is different from the well-known screech tones. Unlike screech, the frequency increases with increasing supply pressure. There is a staging behavior odd harmonic stages occur at lower pressures while the fundamental occurs in a range of relatively higher pressures. A striking feature is that tripping of the nozzle s internal boundary layer tends to suppress the resonance. However, even in the absence of tones the broadband levels are found to be high. That is, relative to a convergent case and at same pressure ratio, the C-D nozzles are found to be noisier, often by more than 10dB. This excess broadband noise (referred to as EBBN) is further explored. Its characteristics are found to be different from the well-known broadband shockassociated noise ( BBSN ). For example, while the frequency of the BBSN peak varies with observation angle no such variation is noted with EBBN. The mechanisms of the transonic tone and the EBBN are not completely understood yet. They appear to be due to unsteady shock motion inside the nozzle. The shock drives the flow downstream like a vibrating diaphragm, and resonance takes place similarly as with acoustic resonance of a conical section having one end closed and the other end open. When the boundary layer is tripped, apparently a breakdown of azimuthal coherence suppresses the resonance. However, there is still unsteady shock motion albeit with superimposed randomness. Such random motion of the internal shock and its interaction with the separated boundary layer produces the EBBN.

Zaman, Khairul B. M. Q.

2009-01-01

44

Turbulence Associated With Broadband Shock Noise in Hot Jets  

NASA Technical Reports Server (NTRS)

Time-Resolved Particle Image Velocimetry (TRPIV) has been applied to a series of jet flows to measure turbulence statistics associated with broadband shock associated noise (BBSN). Data were acquired in jets of Mach numbers 1.05, 1.185, and 1.4 at different temperatures. Both convergent and ideally expanded nozzles were tested, along with a convergent nozzle modified to minimize screech. Key findings include the effect of heat on shock structure and jet decay, the increase in turbulent velocity when screech is present, and the relative lack of spectral detail associated with the enhanced turbulence.

Bridges, James E.; Wernet, Mark P.

2008-01-01

45

Helicopter noise prediction - The current status and future direction  

NASA Technical Reports Server (NTRS)

The paper takes stock of the progress, assesses the current prediction capabilities, and forecasts the direction of future helicopter noise prediction research. The acoustic analogy approach, specifically, theories based on the Ffowcs Williams-Hawkings equations, are the most widely used for deterministic noise sources. Thickness and loading noise can be routinely predicted given good plane motion and blade loading inputs. Blade-vortex interaction noise can also be predicted well with measured input data, but prediction of airloads with the high spatial and temporal resolution required for BVI is still difficult. Current semiempirical broadband noise predictions are useful and reasonably accurate. New prediction methods based on a Kirchhoff formula and direct computation appear to be very promising, but are currently very demanding computationally.

Brentner, Kenneth S.; Farassat, F.

1992-01-01

46

Broadband trailing edge noise from a sharp-edged strut.  

PubMed

This paper presents experimental data concerning the flow and noise generated by a sharp-edged flat plate at low-to-moderate Reynolds number (Reynolds number based on chord of 2.0 × 10(5) to 5.0 × 10(5)). The data are used to evaluate a variety of semi-empirical trailing edge noise prediction methods. All were found to under-predict noise at lower frequencies. Examination of the velocity spectra in the near wake reveals that there are energetic velocity fluctuations at low frequency about the trailing edge. A semi-empirical model of the surface pressure spectrum is derived for predicting the trailing edge noise at low-to-moderate Reynolds number. PMID:21568386

Moreau, Danielle J; Brooks, Laura A; Doolan, Con J

2011-05-01

47

Tandem Cylinder Noise Predictions  

NASA Technical Reports Server (NTRS)

In an effort to better understand landing-gear noise sources, we have been examining a simplified configuration that still maintains some of the salient features of landing-gear flow fields. In particular, tandem cylinders have been studied because they model a variety of component level interactions. The present effort is directed at the case of two identical cylinders spatially separated in the streamwise direction by 3.7 diameters. Experimental measurements from the Basic Aerodynamic Research Tunnel (BART) and Quiet Flow Facility (QFF) at NASA Langley Research Center (LaRC) have provided steady surface pressures, detailed off-surface measurements of the flow field using Particle Image Velocimetry (PIV), hot-wire measurements in the wake of the rear cylinder, unsteady surface pressure data, and the radiated noise. The experiments were conducted at a Reynolds number of 166 105 based on the cylinder diameter. A trip was used on the upstream cylinder to insure a fully turbulent shedding process and simulate the effects of a high Reynolds number flow. The parallel computational effort uses the three-dimensional Navier-Stokes solver CFL3D with a hybrid, zonal turbulence model that turns off the turbulence production term everywhere except in a narrow ring surrounding solid surfaces. The current calculations further explore the influence of the grid resolution and spanwise extent on the flow and associated radiated noise. Extensive comparisons with the experimental data are used to assess the ability of the computations to simulate the details of the flow. The results show that the pressure fluctuations on the upstream cylinder, caused by vortex shedding, are smaller than those generated on the downstream cylinder by wake interaction. Consequently, the downstream cylinder dominates the noise radiation, producing an overall directivity pattern that is similar to that of an isolated cylinder. Only calculations based on the full length of the model span were able to capture the complete decay in the spanwise correlation, thereby producing reasonable noise radiation levels.

Lockhard, David P.; Khorrami, Mehdi R.; CHoudhari, Meelan M.; Hutcheson, Florence V.; Brooks, Thomas F.; Stead, Daniel J.

2007-01-01

48

Acoustic Environment of Admiralty Inlet: Broadband Noise Measurements  

SciTech Connect

Admiralty Inlet has been selected as a potential tidal energy site. It is located near shipping lanes, is a highly variable acoustic environment, and is frequented by the highly endangered southern resident killer whale (SRKW). Resolving environmental impacts is the first step to receiving approval to deploy tidal turbines at Admiralty Inlet. Of particular concern is the potential for blade strike or other negative interactions between the SRKW and the tidal turbine. A variety of technologies including passive and active monitoring systems are being considered as potential tools to determine the presence of SRKW in the vicinity of the turbines. Broadband noise level measurements are critical for the determination of design and operation specifications of all marine and hydrokinetic energy capture technologies. Acoustic environment data at the proposed site was acquired at different depths using a cabled vertical line array (VLA) with four calibrated hydrophones. The sound pressure level (SPL) power spectrum density was estimated based on the fast Fourier transform. This study describes the first broadband SPL measurements for this site at different depths with frequency ranging from 10 kHz to 480 kHz in combination with other information. To understand the SPL caused by this bedload transport, three different pressure sensors with temperature and conductivity were also assembled on the VLA to measure the conditions at the hydrophone deployment depth. The broadband SPL levels at frequency ranges of 3 kHz to 7 kHz as a function of depth were estimated. Only the hydrophone at an average depth of 40 m showed the strong dependence of SPL with distance from the bottom, which was possibly caused by the cobbles shifting on the seabed. Automatic Identification System data were also studied to understand the SPL measurements.

Xu, Jinshan; Deng, Zhiqun; Martinez, Jayson J.; Carlson, Thomas J.; Myers, Joshua R.; Weiland, Mark A.; Jones, Mark E.

2011-09-30

49

Noise Prediction for Maneuvering Rotorcraft  

NASA Technical Reports Server (NTRS)

This paper presents the initial work toward first-principles noise prediction for maneuvering rotors. Both the aeromechanical and acoustics aspects of the maneuver noise problem are discussed. The comprehensive analysis code, CAMRAD 2. was utilized to predict the time-dependent aircraft position and attitude, along - with the rotor blade airloads and motion. The major focus of this effort was the enhancement of the acoustic code WOPWOP necessary to compute the noise from a maneuvering rotorcraft. Full aircraft motion, including arbitrary transient motion, is modeled together with arbitrary rotor blade motions. Noise from a rotorcraft in turning and descending flight is compared to level flight. A substantial increase in the rotor noise is found both for turning flight and during a transient maneuver. Additional enhancements to take advantage of parallel computers and clusters of workstations, in addition to a new compact-chordwise loading formulation, are also described.

Brentner, Kenneth S.; Jones, Henry E.

2000-01-01

50

Turbulence Measurements and Computations for the Predication of Broadband Noise in High Bypass Ratio Fans  

NASA Technical Reports Server (NTRS)

Work was performed under this grant with a view to providing the experimental and computational results needed to improve the prediction of broadband stator noise in large bypass ratio aircraft engines. The central hypothesis of our study was that a large fraction of this noise was generated by the fan tip leakage vortices. More specifically, that these vortices are a significant component of the fan wake turbulence and they contain turbulent eddies of a type that can produce significant broadband noise. To test this hypothesis we originally proposed experimental work and computations with the following objectives: (1) to build a large scale two-dimensional cascade with a tip gap and a stationary endwall that, as far as possible, simulates the fan tip geometry, (2) to build a moving endwall for use with the large scale cascade, (3) to measure, in detail, the turbulence structure and spectrum generated by the blade wake and tip leakage vortex, for both endwall configurations, (4) to use the CFD to compute the flow and turbulence distributions for both the experimental configurations and the ADP fan, (5) to provide the experimental and CFD results for the cascades and the physical understanding gained from their study as a basis for improving the broadband noise prediction method. In large part these objectives have been achieved. The most important achievements and findings of our experimental and computational efforts are summarized below. The bibliography at the end of this report includes a list of all publications produced to date under this project. Note that this list is necessarily incomplete the task of publication (particularly in journal papers) continues.

Devenport, William J.; Ragab, Saad A.

2000-01-01

51

Interim prediction method for fan and compressor source noise  

NASA Technical Reports Server (NTRS)

A method is presented for interim use in assessing the noise generated by fans and compressors in turbojet and turbofan engines. One-third octave band sound pressure levels consisting of broadband, discrete tone, and combination-tone noise components are predicted. Spectral distributions and directivity variations are specified. The method is based on that developed by other investigators with modifications derived from an analysis of full-scale, single-stage fan data. Comparisons of predicted and measured noise performance are presented, and requirements for improving the method are discussed.

Heidmann, M. F.

1975-01-01

52

A Theoretical Basis for the Scaling Law of Broadband Shock Noise Intensity in Supersonic Jets  

NASA Technical Reports Server (NTRS)

A theoretical basis for the scaling of broadband shock noise intensity In supersonic jets was formulated considering linear shock-shear wave interaction. Modeling of broadband shock noise with the aid of shock-turbulence interaction with special reference to linear theories is briefly reviewed. An hypothesis has been postulated that the peak angle of incidence (closer to the critical angle) for the shear wave primarily governs the generation of sound in the interaction process with the noise generation contribution from off-peak incident angles being relatively unimportant. The proposed hypothesis satisfactorily explains the well-known scaling law for the broadband shock-associated noise in supersonic jets.

Kandula, Max

2011-01-01

53

Computation of rotor wake turbulence noise  

Microsoft Academic Search

A major source of fan broadband noise is the interaction of rotor wake turbulence with the fan outlet guide vanes. A broadband noise model that utilizes computed rotor flow turbulence from a Reynolds averaged Navier–Stokes code is used to predict fan broadband noise spectra. The noise model is employed to examine the broadband noise characteristics of the 22-in source diagnostic

M. Nallasamy; E. Envia

2005-01-01

54

Semi-Empirical Modelling of Broadband Noise for Aerofoils  

NASA Astrophysics Data System (ADS)

Turbulence related noise is widely recognized to be one of the most important aerodynamic noise sources for many applications and the development of computational tools for its modelling and prediction is an even more important target in many areas of applied engineering. On a general basis the noise generation mechanisms that can occur on an aerofoil surface can be classified in three main categories: Turbulent Boundary Layer-Trailing Edge noise (TBL-TE), the Laminar Boundary Layer—Vortex Shedding (LBL-VS) noise and the Separation Stall (S-S) noise, respectively related to the boundary layer turbulent eddies, to the boundary layer laminar instabilities and to the large vorticity that can be experienced for different Angle of Attacks, Reynolds and Mach numbers. Despite of the recent improvements of Computational Fluid Dynamics in the frame of turbulence modelling, the numerical computation of high Reynolds flow field turbulence for acoustic purposes is still a hard task to perform as it requires a time-dependant, fully-resolved Large Eddy Simulation often resulting in a prohibitive computational cost. Furthermore in most of the cases it is of fundamental importance to have fast and reliable tools able to capture the driving phenomena and noise sources, in order to be able to perform a large number of simulations embedded in an optimization cycle. The target of this paper is testing the Brooks, Pope and Marcolini semi-empirical model for noise prediction of the NACA 0012 aerofoil on the DU96 geometry in a range of Angle of Attacks from 3 to 10 degrees and Reynolds numbers from 1.5 to 3.1 M. The semi-empirical model input parameters (boundary layer, displacement and momentum thickness) on the suction and pressure side of the aerofoil at the trailing edge location are computed with a steady RANS simulation while the BPM approach has been implemented as an external tool. Computed noise spectra show a good agreement with experimental data from literature in terms of both Sound Pressure Levels (SPLs) and spectra envelope.

De Gennaro, Michele; Kuehnelt, Helmut

2011-09-01

55

Multiple pure tone noise prediction  

NASA Astrophysics Data System (ADS)

This paper presents a fully numerical method for predicting multiple pure tones, also known as “Buzzsaw” noise. It consists of three steps that account for noise source generation, nonlinear acoustic propagation with hard as well as lined walls inside the nacelle, and linear acoustic propagation outside the engine. Noise generation is modeled by steady, part-annulus computational fluid dynamics (CFD) simulations. A linear superposition algorithm is used to construct full-annulus shock/pressure pattern just upstream of the fan from part-annulus CFD results. Nonlinear wave propagation is carried out inside the duct using a pseudo-two-dimensional solution of Burgers' equation. Scattering from nacelle lip as well as radiation to farfield is performed using the commercial solver ACTRAN/TM. The proposed prediction process is verified by comparing against full-annulus CFD simulations as well as against static engine test data for a typical high bypass ratio aircraft engine with hardwall as well as lined inlets. Comparisons are drawn against nacelle unsteady pressure transducer measurements at two axial locations as well as against near- and far-field microphone array measurements outside the duct. This is the first fully numerical approach (no experimental or empirical input is required) to predict multiple pure tone noise generation, in-duct propagation and far-field radiation. It uses measured blade coordinates to calculate MPT noise.

Han, Fei; Sharma, Anupam; Paliath, Umesh; Shieh, Chingwei

2014-12-01

56

Passive geoacoustic inversion with a single hydrophone using broadband ship noise  

E-print Network

Passive geoacoustic inversion with a single hydrophone using broadband ship noise C. Gervaisea) An inversion scheme is proposed, relying upon the inversion of the noise of a moving ship meas- ured. Sound is ubiquitous in the ocean. Ship noise and marine mammal calls can be recorded over great

Paris-Sud XI, Université de

57

Source localization for active control of turbofan rotor-stator broadband noise  

Microsoft Academic Search

In order to identify a reference signal source for an active noise cancellation system, cross-correlation techniques were used to localize broadband noise source regions on exit guide vanes of the NASA Glenn Research Center Advance Noise Control Fan (ANCF). Arrays of surface pressure sensors were imbedded in one guide vane and in the wall of the fan. Synchronous sampling was

Bruce E. Walker

2005-01-01

58

Fan Noise Source Diagnostic Test Computation of Rotor Wake Turbulence Noise  

Microsoft Academic Search

An important source mechanism of fan broadband noise is the interaction of rotor wake turbulence with the fan outlet guide vanes. A broadband noise model that utilizes computed rotor flow turbulence from a RANS code is used to predict fan broadband noise spectra. The noise model is employed to examine the broadband noise characteristics of the 22-inch Source Diagnostic Test

M. Nallasamy; E. Envia; S. A. Thorp; A. Shabbir

2002-01-01

59

Broadband noise characteristics of a model counter-rotating shrouded propfan  

NASA Astrophysics Data System (ADS)

In recent years counter-rotating propfan aeroengines were developed since they promise significant fuel savings compared to conventional fan engines. The German manufacturer MTU has developed the CRISP (Counter-Rotating Integrated Shrouded Propfan) 1:6.25-scale model engine which has been tested in the German Dutch Wind Tunnel (DNW). The present study concentrates on the broadband noise component and its relative importance to the total sound emission. While single-propeller/propfan noise emission is dominated by rotational noise, a counter-rotating propfan may constitute a significant source of broadband noise.

Boettcher, Jan; Dobrzynski, Werner; Gehlhar, Burkhard

60

Broadband squeezing of quantum noise in a Michelson interferometer with Twin-Signal-Recycling  

E-print Network

Twin-Signal-Recycling (TSR) builds on the resonance doublet of two optically coupled cavities and efficiently enhances the sensitivity of an interferometer at a dedicated signal frequency. We report on the first experimental realization of a Twin-Signal-Recycling Michelson interferometer and also its broadband enhancement by squeezed light injection. The complete setup was stably locked and a broadband quantum noise reduction of the interferometers shot noise by a factor of up to 4\\,dB was demonstrated. The system was characterized by measuring its quantum noise spectra for several tunings of the TSR cavities. We found good agreement between the experimental results and numerical simulations.

André Thüring; Christian Gräf; Henning Vahlbruch; Moritz Mehmet; Karsten Danzmann; Roman Schnabel

2010-05-25

61

On the Scaling Law for Broadband Shock Noise Intensity in Supersonic Jets  

NASA Technical Reports Server (NTRS)

A theoretical model for the scaling of broadband shock noise intensity in supersonic jets was formulated on the basis of linear shock-shear wave interaction. An hypothesis has been postulated that the peak angle of incidence (closer to the critical angle) for the shear wave primarily governs the generation of sound in the interaction process rather than the noise generation contribution from off-peak incident angles. The proposed theory satisfactorily explains the well-known scaling law for the broadband shock -associated noise in supersonic jets.

Kanudula, Max

2009-01-01

62

NASA progress in aircraft noise prediction  

NASA Technical Reports Server (NTRS)

Langley Research Center efforts to develop a methodology for predicting the effective perceived noise level (EPNL) produced by jet-powered CTOL aircraft to an accuracy of + or - 1.5 dB are summarized with emphasis on the aircraft noise prediction program (ANOPP) which contains a complete set of prediction methods for CTOL aircraft including propulsion system noise sources, aerodynamic or airframe noise sources, forward speed effects, a layered atmospheric model with molecular absorption, ground impedance effects including excess ground attenuation, and a received noise contouring capability. The present state of ANOPP is described and its accuracy and applicability to the preliminary aircraft design process is assessed. Areas are indicated where further theoretical and experimental research on noise prediction are needed. Topics covered include the elements of the noise prediction problem which are incorporated in ANOPP, results of comparisons of ANOPP calculations with measured noise levels, and progress toward treating noise as a design constraint in aircraft system studies.

Raney, J. P.; Padula, S. L.; Zorumski, W. E.

1981-01-01

63

NASA progress in aircraft noise prediction  

NASA Technical Reports Server (NTRS)

Some of the essential features of aircraft noise prediction are described and the basis for evaluating its capability and future potential is discussed. A takeoff noise optimizing procedure is described which calculates a minimum noise takeoff procedure subject to multiple site noise constraints.

Raney, J. P.; Padula, S. L.; Zorumski, W. E.

1981-01-01

64

Secure communication in fiber optic systems via transmission of broad-band optical noise.  

PubMed

We propose a new scheme for data encryption in the physical layer. Our scheme is based on the distribution of a broadband optical noise-like signal between Alice and Bob. The broadband signal is used for the establishment of a secret key that can be used for the secure transmission of information by using the one-time-pad method. We characterize the proposed scheme and study its applicability to the existing fiber-optics communications infrastructure. PMID:18542430

Buskila, O; Eyal, A; Shtaif, M

2008-03-01

65

Anechoic wind tunnel study of turbulence effects on wind turbine broadband noise  

NASA Technical Reports Server (NTRS)

This paper describes recent results obtained at MIT on the experimental and theoretical modelling of aerodynamic broadband noise generated by a downwind rotor horizontal axis wind turbine. The aerodynamic broadband noise generated by the wind turbine rotor is attributed to the interaction of ingested turbulence with the rotor blades. The turbulence was generated in the MIT anechoic wind tunnel facility with the aid of biplanar grids of various sizes. The spectra and the intensity of the aerodynamic broadband noise have been studied as a function of parameters which characterize the turbulence and of wind turbine performance parameters. Specifically, the longitudinal integral scale of turbulence, the size scale of turbulence, the number of turbine blades, and free stream velocity were varied. Simultaneous measurements of acoustic and turbulence signals were made. The sound pressure level was found to vary directly with the integral scale of the ingested turbulence but not with its intensity level. A theoretical model based on unsteady aerodynamics is proposed.

Loyd, B.; Harris, W. L.

1995-01-01

66

Prediction of Externally Blown Flap Noise and Turbomachinery Strut Noise  

NASA Technical Reports Server (NTRS)

Methods were developed for predicting externally blown flap (EBF) noise and turbomachinery strut noise. Noise radiated by under-the-wing and upper-surface-blowing EBF configurations is calculated as a sum of lift dipole noise, trailing edge noise, and jet quadrupole noise. Resulting predictions of amplitudes and spectra generally were in good agreement with data from small-scale models. These data cover a range of exhaust velocity, flap deflection, exhaust nozzle position, exhaust nozzle shape, and ratio of exhaust nozzle diameter to wing chord. A semi-empirical method for predicting dipole noise radiation from a strut with incident turbulence was in good agreement with data. Leading-edge regions made of perforated plate backed by a bulk acoustic absorber achieved up to 7 db reduction of strut noise caused by incident turbulence at high frequencies. Radial turbulence in a turbofan exit duct was found to have a relatively high level associated with the mean velocity defect in the rotor blade wakes. Use of these turbulence spectra and a dipole noise radiation equation gave general prediction of measured aft-radiated sound power caused by a splitter ring in a full-scale fan exit duct.

Fink, M. R.

1975-01-01

67

Computer program to predict aircraft noise levels  

NASA Technical Reports Server (NTRS)

Methods developed at the NASA Lewis Research Center for predicting the noise contributions from various aircraft noise sources were programmed to predict aircraft noise levels either in flight or in ground tests. The noise sources include fan inlet and exhaust, jet, flap (for powered lift), core (combustor), turbine, and airframe. Noise propagation corrections are available for atmospheric attenuation, ground reflections, extra ground attenuation, and shielding. Outputs can include spectra, overall sound pressure level, perceived noise level, tone-weighted perceived noise level, and effective perceived noise level at locations specified by the user. Footprint contour coordinates and approximate footprint areas can also be calculated. Inputs and outputs can be in either System International or U.S. customary units. The subroutines for each noise source and propagation correction are described. A complete listing is given.

Clark, B. J.

1981-01-01

68

Broadband Shock Noise in Internally-Mixed Dual-Stream Jets  

NASA Technical Reports Server (NTRS)

Broadband shock noise (BBSN) has been studied in some detail in single-flow jets and recently in dual-stream jets with separate flow exhaust systems. Shock noise is of great concern in these latter cases because of the noise created for the aircraft cabin by the underexpanded nozzle flow at cruise. Another case where shock noise is of concern is in the case of future supersonic aircraft that are expected to have bypass ratios small enough to justify internally mixed exhaust systems, and whose mission will push cycles to the point of imperfectly expanded flows. Dual-stream jets with internally mixed plume have some simplifying aspects relative to the separate flow jets, having a single shock structure given by the common nozzle pressure. This is used to separate the contribution of the turbulent shear layer to the broadband shock noise. Shock structure is held constant while the geometry and strength of the inner and merged shear layers are varying by changing splitter area ratio and core stream temperature. Flow and noise measurements are presented which document the efforts at separating the contribution of the inner shear layer to the broadband shock noise.

Bridges, James E.

2009-01-01

69

The amplification of broadband jet noise by pure tone excitation  

Microsoft Academic Search

It was found experimentally that broad band jet noise can be amplified as much as 6 to 7 dB. The jet noise amplification effect takes place at sound pressure levels present in real aircraft engines. The experimental investigation was restricted to a cold jet at high subsonic Mach numbers excited by a plane sound wave coming from inside the nozzle.

D. Bechert; E. Pfizenmaier

1975-01-01

70

Aircraft noise prediction program theoretical manual: Rotorcraft System Noise Prediction System (ROTONET), part 4  

Microsoft Academic Search

This document describes the theoretical methods used in the rotorcraft noise prediction system (ROTONET), which is a part of the NASA Aircraft Noise Prediction Program (ANOPP). The ANOPP code consists of an executive, database manager, and prediction modules for jet engine, propeller, and rotor noise. The ROTONET subsystem contains modules for the prediction of rotor airloads and performance with momentum

Donald S. Weir; Stephen J. Jumper; Casey L. Burley; Robert A. Golub

1995-01-01

71

Fan Noise Prediction: Status and Needs  

NASA Technical Reports Server (NTRS)

The prediction of fan noise is an important part to the prediction of overall turbofan engine noise. Advances in computers and better understanding of the flow physics have allowed researchers to compute sound generation from first principles and rely less on empirical correlations. While progress has been made, there are still many aspects of the problem that need to be explored. This paper presents some recent advances in fan noise prediction and suggests areas that still need further development. Fan noise predictions that support the recommendations are taken from existing publications.

Huff, Dennis L.

1997-01-01

72

Prediction of Traffic Noise: A Screening Technique  

Microsoft Academic Search

Traffic noise is ubiquitous in many communities and is an important environmental concern, especially for persons located near major roadways. Several different methods are available to estimate noise levels resulting from roadway traffic. These include computational, graphical, and computer modeling techniques.The prediction methodology presented here is a simplified technique that can be used for estimating noise resulting from traffic and

Michael J. Barboza; P. E. DEE; Sharon Paul Carpenter; Leslie E. Roche

1995-01-01

73

Prediction of Jet Noise Shielding Dimitri Papamoschou*  

E-print Network

Prediction of Jet Noise Shielding Dimitri Papamoschou* University of California, Irvine, CA 92697, USA This study is motivated by the development of aircraft that use jet noise shielding for diffraction of sound from omnidirectional point sources. However, the jet noise source is distributed

Papamoschou, Dimitri

74

The prediction of flow-induced noise in heat exchanger tube arrays  

Microsoft Academic Search

A number of methods for the prediction of flow-induced acoustic standing waves in heat exchangers are recommended in the literature. The source for this noise has been assumed to be vortex shedding, turbulent buffeting or broadband turbulence, and a variety of methods based on these have been proposed for predicting the occurrence of these standing-wave resonances. Furthermore, parameters which estimate

J. A. Fitzpatrick

1985-01-01

75

The flux-dependent amplitude of broadband noise variability in X-ray binaries and active galaxies  

E-print Network

Standard shot-noise models, which seek to explain the broadband noise variability that characterises the X-ray lightcurves of X-ray binaries and active galaxies, predict that the power spectrum of the X-ray lightcurve is stationary (i.e. constant amplitude and shape) on short time-scales. We show that the broadband noise power spectra of the black hole candidate Cyg X-1 and the accreting millisecond pulsar SAX J1808.4-3658 are intrinsically non-stationary, in that RMS variability scales linearly with flux. Flux-selected power spectra confirm that this effect is due to changes in power-spectral amplitude and not shape. The lightcurves of three Seyfert galaxies are also consistent with a linear relationship between RMS variability and flux, suggesting that it is an intrinsic feature of the broadband noise variability in compact accreting systems over more than 6 decades of central object mass. The RMS variability responds to flux variations on all measured time-scales, raising fundamental difficulties for shot-noise models which seek to explain this result by invoking variations in the shot parameters. We suggest that models should be explored where the longest time-scale variations are fundamental and precede the variations on shorter time-scales. Possible models which can explain the linear RMS-flux relation include the fractal break-up of large coronal flares, or the propagation of fluctuations in mass accretion rate through the accretion disk. The linear relationship between RMS variability and flux in Cyg X-1 and SAX J1808.4-3658 is offset on the flux axis, suggesting the presence of a second, constant-flux component to the lightcurve which contributes 25% of the total flux. The spectrum of this constant component is similar to the total spectrum [abridged].

Philip Uttley; Ian M. McHardy

2001-03-22

76

Flyover-noise measurement and prediction  

NASA Technical Reports Server (NTRS)

Details are presented for the measurement and prediction of aircraft flyover noise to be used for certification, research and development, community noise surveys, airport monitors, and pass fail criteria. Test details presented are applicable to all types of aircraft, both large and small, and the use of Federal Aviation Regulations (FAR) Part 36 (ref. 1) is emphasized. Accuracy of noise measurements is important. Thus, a pass-fail criterion should be used for all noise measurements. Finally, factors which influence the sound propagation and noise prediction procedures, such as atmospheric and ground effects, are also presented.

Peart, Noel A.

1991-01-01

77

Fan Noise Prediction with Applications to Aircraft System Noise Assessment  

NASA Technical Reports Server (NTRS)

This paper describes an assessment of current fan noise prediction tools by comparing measured and predicted sideline acoustic levels from a benchmark fan noise wind tunnel test. Specifically, an empirical method and newly developed coupled computational approach are utilized to predict aft fan noise for a benchmark test configuration. Comparisons with sideline noise measurements are performed to assess the relative merits of the two approaches. The study identifies issues entailed in coupling the source and propagation codes, as well as provides insight into the capabilities of the tools in predicting the fan noise source and subsequent propagation and radiation. In contrast to the empirical method, the new coupled computational approach provides the ability to investigate acoustic near-field effects. The potential benefits/costs of these new methods are also compared with the existing capabilities in a current aircraft noise system prediction tool. The knowledge gained in this work provides a basis for improved fan source specification in overall aircraft system noise studies.

Nark, Douglas M.; Envia, Edmane; Burley, Casey L.

2009-01-01

78

Broadband maximum likelihood estimation of shallow ocean parameters using shipping noise  

Microsoft Academic Search

Environmental parameter estimation for a shallow ocean is addressed by using wideband shipping noise as a source of acoustic energy. Unknown locations of the broadband acoustic sources are estimated simultaneously with the ocean depth using the approximate conditional maximum likelihood estimator (CMLE). This procedure is tested via computer simulations and applied to the experimental hydrophone towed array data

C. F. Mecklenbrauker; A. Gershman

2001-01-01

79

Empirical Prediction of Aircraft Landing Gear Noise  

NASA Technical Reports Server (NTRS)

This report documents a semi-empirical/semi-analytical method for landing gear noise prediction. The method is based on scaling laws of the theory of aerodynamic noise generation and correlation of these scaling laws with current available test data. The former gives the method a sound theoretical foundation and the latter quantitatively determines the relations between the parameters of the landing gear assembly and the far field noise, enabling practical predictions of aircraft landing gear noise, both for parametric trends and for absolute noise levels. The prediction model is validated by wind tunnel test data for an isolated Boeing 737 landing gear and by flight data for the Boeing 777 airplane. In both cases, the predictions agree well with data, both in parametric trends and in absolute noise levels.

Golub, Robert A. (Technical Monitor); Guo, Yue-Ping

2005-01-01

80

Highway traffic noise prediction based on GIS  

NASA Astrophysics Data System (ADS)

Before building a new road, we need to predict the traffic noise generated by vehicles. Traditional traffic noise prediction methods are based on certain locations and they are not only time-consuming, high cost, but also cannot be visualized. Geographical Information System (GIS) can not only solve the problem of manual data processing, but also can get noise values at any point. The paper selected a road segment from Wenxi to Heyang. According to the geographical overview of the study area and the comparison between several models, we combine the JTG B03-2006 model and the HJ2.4-2009 model to predict the traffic noise depending on the circumstances. Finally, we interpolate the noise values at each prediction point and then generate contours of noise. By overlaying the village data on the noise contour layer, we can get the thematic maps. The use of GIS for road traffic noise prediction greatly facilitates the decision-makers because of GIS spatial analysis function and visualization capabilities. We can clearly see the districts where noise are excessive, and thus it becomes convenient to optimize the road line and take noise reduction measures such as installing sound barriers and relocating villages and so on.

Zhao, Jianghua; Qin, Qiming

2014-05-01

81

Fan broadband noise shielding for over-wing engines  

NASA Astrophysics Data System (ADS)

Increasingly demanding community noise targets are promoting noise performance ever higher on the list of airliner design drivers. In response, significant noise reductions are being made, though at a declining rate—it appears that a whole airframe approach is now needed to achieve significant further gains. As a possible step in this direction, over-wing engine installations are considered here, which use the airframe itself as a noise shield. The paper is the account of an experimental investigation of the comparative shielding performances of a range of relative engine positions on such a layout. Using the statistical modelling technique Kriging, we build an approximation of the noise shielding metric as a function of the position of the engines above the wing—this can serve as the input to multi-disciplinary design trade-off studies. We then compare the results found with the results of applying simple half-barrier diffraction theory to the same problem. We conclude that the latter could be considered as a first order, conceptual design tool, though it misses certain features of the design merit landscape identified by the experiment presented here.

Powell, Stephen; Sóbester, András; Joseph, Phillip

2012-11-01

82

Hybrid phononic crystals for broad-band frequency noise control by sound blocking and localization.  

PubMed

A bandgap cannot be enlarged sufficiently enough to suppress a broad-band noise only with a single type of finite-length phononic crystals. Here, a hybrid phononic crystal consisting of a bi-prism and an inverted bi-prism is proposed for noise control in a broad band; a stop band is formed in a central frequency range while positive-positive and positive-negative refractions occur in lower and higher frequency ranges to concentrate acoustic energy in a central localized zone. Thereby, the remaining zone becomes little affected by the noise. Analysis and numerical simulations are given for the justification of the proposed configuration. PMID:23145703

Yoo, Sungmin; Kim, Yoon Jae; Kim, Yoon Young

2012-11-01

83

Modeling and Prediction of Fan Noise  

NASA Technical Reports Server (NTRS)

Fan noise is a significant contributor to the total noise signature of a modern high bypass ratio aircraft engine and with the advent of ultra high bypass ratio engines like the geared turbofan, it is likely to remain so in the future. As such, accurate modeling and prediction of the basic characteristics of fan noise are necessary ingredients in designing quieter aircraft engines in order to ensure compliance with ever more stringent aviation noise regulations. In this paper, results from a comprehensive study aimed at establishing the utility of current tools for modeling and predicting fan noise will be summarized. It should be emphasized that these tools exemplify present state of the practice and embody what is currently used at NASA and Industry for predicting fan noise. The ability of these tools to model and predict fan noise is assessed against a set of benchmark fan noise databases obtained for a range of representative fan cycles and operating conditions. Detailed comparisons between the predicted and measured narrowband spectral and directivity characteristics of fan nose will be presented in the full paper. General conclusions regarding the utility of current tools and recommendations for future improvements will also be given.

Envia, Ed

2008-01-01

84

Landing gear and cavity noise prediction  

NASA Technical Reports Server (NTRS)

Prediction of airframe noise radiation from the landing gear and wheel wells of commercial aircraft is examined. Measurements of these components on typical aircraft are presented and potential noise sources identified. Semiempirical expressions for the sound generation by these sources are developed from available experimental data and theoretical analyses. These expressions are employed to estimate the noise radiation from the landing gear and wheel wells for a typical aircraft and to rank order the component sources.

Bliss, D. B.; Hayden, R. E.

1976-01-01

85

Shielding of Turbomachinery Broadband Noise from a Hybrid Wing Body Aircraft Configuration  

NASA Technical Reports Server (NTRS)

The results of an experimental study on the effects of engine placement and vertical tail configuration on shielding of exhaust broadband noise radiation are presented. This study is part of the high fidelity aeroacoustic test of a 5.8% scale Hybrid Wing Body (HWB) aircraft configuration performed in the 14- by 22-Foot Subsonic Tunnel at NASA Langley Research Center. Broadband Engine Noise Simulators (BENS) were used to determine insertion loss due to shielding by the HWB airframe of the broadband component of turbomachinery noise for different airframe configurations and flight conditions. Acoustics data were obtained from flyover and sideline microphones traversed to predefined streamwise stations. Noise measurements performed for different engine locations clearly show the noise benefit associated with positioning the engine nacelles further upstream on the HWB centerbody. Positioning the engine exhaust 2.5 nozzle diameters upstream (compared to 0.5 nozzle diameters downstream) of the HWB trailing edge was found of particular benefit in this study. Analysis of the shielding performance obtained with and without tunnel flow show that the effectiveness of the fuselage shielding of the exhaust noise, although still significant, is greatly reduced by the presence of the free stream flow compared to static conditions. This loss of shielding is due to the turbulence in the model near-wake/boundary layer flow. A comparison of shielding obtained with alternate vertical tail configurations shows limited differences in level; nevertheless, overall trends regarding the effect of cant angle and vertical location are revealed. Finally, it is shown that the vertical tails provide a clear shielding benefit towards the sideline while causing a slight increase in noise below the aircraft.

Hutcheson, Florence V.; Brooks, Thomas F.; Burley, Casey L.; Bahr, Christopher J.; Stead, Daniel J.; Pope, D. Stuart

2014-01-01

86

Assessment of NASA's Aircraft Noise Prediction Capability  

NASA Technical Reports Server (NTRS)

A goal of NASA s Fundamental Aeronautics Program is the improvement of aircraft noise prediction. This document provides an assessment, conducted from 2006 to 2009, on the current state of the art for aircraft noise prediction by carefully analyzing the results from prediction tools and from the experimental databases to determine errors and uncertainties and compare results to validate the predictions. The error analysis is included for both the predictions and the experimental data and helps identify where improvements are required. This study is restricted to prediction methods and databases developed or sponsored by NASA, although in many cases they represent the current state of the art for industry. The present document begins with an introduction giving a general background for and a discussion on the process of this assessment followed by eight chapters covering topics at both the system and the component levels. The topic areas, each with multiple contributors, are aircraft system noise, engine system noise, airframe noise, fan noise, liner physics, duct acoustics, jet noise, and propulsion airframe aeroacoustics.

Dahl, Milo D. (Editor)

2012-01-01

87

Aircraft noise prediction program theoretical manual, part 2  

NASA Technical Reports Server (NTRS)

Detailed prediction methods for specific aircraft noise sources are given. These sources are airframe noise, combustion noise, fan noise, single and dual stream jet noise, and turbine noise. Modifications to the NASA methods which comply with the International Civil Aviation Organization standard method for aircraft noise prediction are given.

Zorumski, W. E.

1982-01-01

88

Source localization for active control of turbofan rotor-stator broadband noise  

NASA Astrophysics Data System (ADS)

In order to identify a reference signal source for an active noise cancellation system, cross-correlation techniques were used to localize broadband noise source regions on exit guide vanes of the NASA Glenn Research Center Advance Noise Control Fan (ANCF). Arrays of surface pressure sensors were imbedded in one guide vane and in the wall of the fan. Synchronous sampling was used with a multichannel data acquisition system to allow removal of periodic components from the signals. The signals were then cross-correlated to assess radiation directivity and the relationship between vane surface pressure and in-duct acoustic noise. The results of these measurements indicated that broadband unsteady pressures near the leading edge tip of the guide vane were well enough correlated with acoustic radiation that 2-3 dB active noise cancellation could be achieved using a simple gain-delay control algorithm and actuator array. After successful simulation in a wind tunnel environment the concept was incorporated on 15 guide vanes and tested in ANCF. Cross-correlation measurements were further used to evaluate system performance and to identify competing noises from rotating and stationary sources within the fan.

Walker, Bruce E.

2005-09-01

89

An Assessment of Current Fan Noise Prediction Capability  

NASA Technical Reports Server (NTRS)

In this paper, the results of an extensive assessment exercise carried out to establish the current state of the art for predicting fan noise at NASA are presented. Representative codes in the empirical, analytical, and computational categories were exercised and assessed against a set of benchmark acoustic data obtained from wind tunnel tests of three model scale fans. The chosen codes were ANOPP, representing an empirical capability, RSI, representing an analytical capability, and LINFLUX, representing a computational aeroacoustics capability. The selected benchmark fans cover a wide range of fan pressure ratios and fan tip speeds, and are representative of modern turbofan engine designs. The assessment results indicate that the ANOPP code can predict fan noise spectrum to within 4 dB of the measurement uncertainty band on a third-octave basis for the low and moderate tip speed fans except at extreme aft emission angles. The RSI code can predict fan broadband noise spectrum to within 1.5 dB of experimental uncertainty band provided the rotor-only contribution is taken into account. The LINFLUX code can predict interaction tone power levels to within experimental uncertainties at low and moderate fan tip speeds, but could deviate by as much as 6.5 dB outside the experimental uncertainty band at the highest tip speeds in some case.

Envia, Edmane; Woodward, Richard P.; Elliott, David M.; Fite, E. Brian; Hughes, Christopher E.; Podboy, Gary G.; Sutliff, Daniel L.

2008-01-01

90

Assessment of Current Jet Noise Prediction Capabilities  

NASA Technical Reports Server (NTRS)

An assessment was made of the capability of jet noise prediction codes over a broad range of jet flows, with the objective of quantifying current capabilities and identifying areas requiring future research investment. Three separate codes in NASA s possession, representative of two classes of jet noise prediction codes, were evaluated, one empirical and two statistical. The empirical code is the Stone Jet Noise Module (ST2JET) contained within the ANOPP aircraft noise prediction code. It is well documented, and represents the state of the art in semi-empirical acoustic prediction codes where virtual sources are attributed to various aspects of noise generation in each jet. These sources, in combination, predict the spectral directivity of a jet plume. A total of 258 jet noise cases were examined on the ST2JET code, each run requiring only fractions of a second to complete. Two statistical jet noise prediction codes were also evaluated, JeNo v1, and Jet3D. Fewer cases were run for the statistical prediction methods because they require substantially more resources, typically a Reynolds-Averaged Navier-Stokes solution of the jet, volume integration of the source statistical models over the entire plume, and a numerical solution of the governing propagation equation within the jet. In the evaluation process, substantial justification of experimental datasets used in the evaluations was made. In the end, none of the current codes can predict jet noise within experimental uncertainty. The empirical code came within 2dB on a 1/3 octave spectral basis for a wide range of flows. The statistical code Jet3D was within experimental uncertainty at broadside angles for hot supersonic jets, but errors in peak frequency and amplitude put it out of experimental uncertainty at cooler, lower speed conditions. Jet3D did not predict changes in directivity in the downstream angles. The statistical code JeNo,v1 was within experimental uncertainty predicting noise from cold subsonic jets at all angles, but did not predict changes with heating of the jet and did not account for directivity changes at supersonic conditions. Shortcomings addressed here give direction for future work relevant to the statistical-based prediction methods. A full report will be released as a chapter in a NASA publication assessing the state of the art in aircraft noise prediction.

Hunter, Craid A.; Bridges, James E.; Khavaran, Abbas

2008-01-01

91

A rod-airfoil experiment as a benchmark for broadband noise modeling  

Microsoft Academic Search

A low Mach number rod-airfoil experiment is shown to be a good benchmark for numerical and theoretical broadband noise modeling. The benchmarking approach is applied to a sound computation from a 2D unsteady-Reynolds-averaged Navier–Stokes (U-RANS) flow field, where 3D effects are partially compensated for by a spanwise statistical model and by a 3D large eddy simulation. The experiment was conducted

Marc C. Jacob; Jérôme Boudet; Damiano Casalino; Marc Michard

2005-01-01

92

Ambient noise recorded at broadband stations in Portugal and Morocco: Characterization and Sources  

NASA Astrophysics Data System (ADS)

The first broadband (BB) seismic stations were deployed in Portugal in the 1990s, and ever since their number had steadily increased. Portugal is currently covered by a network of 35 broadband stations in mainland Portugal, which is complemented by stations in the islands of Madeira and Azores, as well as stations in Morocco. In the period 2010 - 2012, project WILAS - "West Iberia Lithosphere and Astenosphere Structure" (PTDC/CTE-GIX/097946/2008), deployed 30 additional temporary seismic BB stations in mainland Portugal. The WILAS stations, in addition to the permanent and TOPOIBERIA stations, provided a full and dense coverage of the Iberian Peninsula. In this presentation we will characterize the ambient seismic noise recorded at BB stations deployed in Portugal (mainland, Azores and Madeira) and Morocco. We analyse all time periods of data available since the instruments were installed. The noise is characterized by means of probability density functions (PDFs) of power spectral density (PSDs) of continuous, overlapping, 1-hour segments of data. Time-series of noise levels at different frequencies and spectrograms are computed to visualize the variations of ambient noise over different time periods and frequency bands. We observe the expected diurnal periodicity at high frequencies and seasonal variation at long periods. There is a clear increase of the noise amplitude in the microseismic band during the Winter, when more storms occur in the adjacent Northern Atlantic. We correlate sea level, storm activity, and other atmospheric parameters with the variations in ambient noise level. The analysis performed gives clues concerning data quality (poor quality data is clearly identified), Earth structure (a correlation is visible between sedimentary basins and amplification of seismic noise), and sources of ambient noise at different frequency bands.

Custódio, Susana; Madureira, Guilherme; Corela, Carlos; Alves, Paulo; Haberland, Christian; Carrilho, Fernando; Fonseca, Joao; Caldeira, Bento; Dias, Nuno

2013-04-01

93

Advances in tilt rotor noise prediction  

NASA Technical Reports Server (NTRS)

The two most serious tilt rotor external noise problems, hover noise and blade-vortex interaction noise, are studied. The results of flow visualization and inflow velocity measurements document a complex, recirculating highly unsteady and turbulent flow due to the rotor-wing-body interactions characteristic of tilt rotors. The wing under the rotor is found to obstruct the inflow, causing a deficit in the inflow velocities over the inboard region of the rotor. Discrete frequency harmonic thickness and loading noise mechanisms in hover are examined by first modeling tilt rotor hover aerodynamics and then applying various noise prediction methods using the WOPWOP code. The analysis indicates that the partial ground plane created by the wing below the rotor results in a primary sound source for hover.

George, A. R.; Coffen, C. D.; Ringler, T. D.

1992-01-01

94

Numerical assessment for a broadband and tuned noise using hybrid mufflers and a simulated annealing method  

NASA Astrophysics Data System (ADS)

A broadband noise hybridized with pure tones often occurs in practical engineering work. However, assessments of a muffler's optimal shape design that would simultaneously overcome a broadband noise hybridized with multiple tones within a constrained space were rarely addressed. In order to promote the best acoustical performance in mufflers, five kinds of the hybrid mufflers composed of a reactive unit, a dissipative unit, and Helmholtz resonator (HR) units will be proposed. Moreover, to strengthen the noise elimination at the pure tone, mufflers having parallel multiple-sectioned HRs or having multiple HR connections in series (muffler D and muffler E) will be also presented in the noise abatement. On the basis of the plane wave theory, the four-pole system matrix used to evaluate the acoustic performance of a multi-tone hybrid Helmholtz muffler will be presented. A numerical case for eliminating broadband noise hybridized with a pure tone emitted from a machine room using five kinds of mufflers (muffler A-E) will also be introduced. To find the best acoustical performance of a space-constrained muffler, a numerical assessment using a simulated annealing (SA) method is adopted. To verify the availability of the SA optimization, a numerical optimization of muffler A at a pure tone (280 Hz) is exemplified. Before the SA operation can be carried out, the accuracy of the mathematical model will be checked using the experimental data. The influences of the sound transmission loss (STL) with respect to N1-array HR and the STL with respect to one-array HR sectioned in N2 divisions have also been assessed. Also, the influence of the STL with respect to the design parameters such as the ratio of d1/d2, the diameter of the perforated hole (dH), the porosity (p%) of the perforated plate, and the outer diameter (d2) of the dissipative unit has been analyzed. Consequently, a successful approach in eliminating a broadband noise hybridized with a pure tone using optimally shaped hybrid mufflers and a simulated annealing method within a constrained space has been demonstrated.

Chiu, Min-Chie

2013-06-01

95

Continuous production of glass-coated microwires and the applications for broadband noise suppression composite sheets  

NASA Astrophysics Data System (ADS)

A system and a method were developed for continuous production of glass-coated microwires with controllable glass thickness and metallic core diameter. Fe-Si-Al flakes were fabricated by planetary ball milling using ethanol as a dispersant. A composite noise suppression sheet was prepared with glass-coated microwires combined with Fe-Si-Al flakes. The characteristics of the conduction noise suppression of the composite sheet were evaluated on a microstrip line in gigahertz frequencies. The conduction electromagnetic noise was effectively suppressed by the composite sheet in broad-band frequency region; the power loss is greater than 70% in the frequency range from 0.7 to 8.5 GHz.

Li, Deren; Liu, Tiancheng; Li, Jianliang; Chen, Zheng; Liu, Kaihuang; Lu, Zhichao; Zhou, Shaoxiong

2012-05-01

96

Predictions of Supersonic Jet Mixing and Shock-Associated Noise Compared With Measured Far-Field Data  

NASA Technical Reports Server (NTRS)

Codes for predicting supersonic jet mixing and broadband shock-associated noise were assessed using a database containing noise measurements of a jet issuing from a convergent nozzle. Two types of codes were used to make predictions. Fast running codes containing empirical models were used to compute both the mixing noise component and the shock-associated noise component of the jet noise spectrum. One Reynolds-averaged, Navier-Stokes-based code was used to compute only the shock-associated noise. To enable the comparisons of the predicted component spectra with data, the measured total jet noise spectra were separated into mixing noise and shock-associated noise components. Comparisons were made for 1/3-octave spectra and some power spectral densities using data from jets operating at 24 conditions covering essentially 6 fully expanded Mach numbers with 4 total temperature ratios.

Dahl, Milo D.

2010-01-01

97

Jet Noise Diagnostics Supporting Statistical Noise Prediction Methods  

NASA Technical Reports Server (NTRS)

The primary focus of my presentation is the development of the jet noise prediction code JeNo with most examples coming from the experimental work that drove the theoretical development and validation. JeNo is a statistical jet noise prediction code, based upon the Lilley acoustic analogy. Our approach uses time-average 2-D or 3-D mean and turbulent statistics of the flow as input. The output is source distributions and spectral directivity. NASA has been investing in development of statistical jet noise prediction tools because these seem to fit the middle ground that allows enough flexibility and fidelity for jet noise source diagnostics while having reasonable computational requirements. These tools rely on Reynolds-averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) solutions as input for computing far-field spectral directivity using an acoustic analogy. There are many ways acoustic analogies can be created, each with a series of assumptions and models, many often taken unknowingly. And the resulting prediction can be easily reverse-engineered by altering the models contained within. However, only an approach which is mathematically sound, with assumptions validated and modeled quantities checked against direct measurement will give consistently correct answers. Many quantities are modeled in acoustic analogies precisely because they have been impossible to measure or calculate, making this requirement a difficult task. The NASA team has spent considerable effort identifying all the assumptions and models used to take the Navier-Stokes equations to the point of a statistical calculation via an acoustic analogy very similar to that proposed by Lilley. Assumptions have been identified and experiments have been developed to test these assumptions. In some cases this has resulted in assumptions being changed. Beginning with the CFD used as input to the acoustic analogy, models for turbulence closure used in RANS CFD codes have been explored and compared against measurements of mean and rms velocity statistics over a range of jet speeds and temperatures. Models for flow parameters used in the acoustic analogy, most notably the space-time correlations of velocity, have been compared against direct measurements, and modified to better fit the observed data. These measurements have been extremely challenging for hot, high speed jets, and represent a sizeable investment in instrumentation development. As an intermediate check that the analysis is predicting the physics intended, phased arrays have been employed to measure source distributions for a wide range of jet cases. And finally, careful far-field spectral directivity measurements have been taken for final validation of the prediction code. Examples of each of these experimental efforts will be presented. The main result of these efforts is a noise prediction code, named JeNo, which is in middevelopment. JeNo is able to consistently predict spectral directivity, including aft angle directivity, for subsonic cold jets of most geometries. Current development on JeNo is focused on extending its capability to hot jets, requiring inclusion of a previously neglected second source associated with thermal fluctuations. A secondary result of the intensive experimentation is the archiving of various flow statistics applicable to other acoustic analogies and to development of time-resolved prediction methods. These will be of lasting value as we look ahead at future challenges to the aeroacoustic experimentalist.

Bridges, James E.

2006-01-01

98

Railway Noise Prediction Models: a Comparison  

NASA Astrophysics Data System (ADS)

This paper represents a comparison between some European prediction models for rail traffic noise. These models are from Austria, Denmark, France, Germany, The Netherlands, Norway, Sweden, Switzerland and the U.K. In the propagation part the ISO 9613-2 is also considered. The comparison of the noise emission gives results for disc- and block-braked passenger trains and for freight trains. For purposes of comparison the propagation model is divided according to the usual attenuation elements including geometrical spreading, atmospheric attenuation, ground attenuation, screening attenuation and reflections. These attenuation effects are compared separately.

VAN LEEUWEN, H. J. A.

2000-03-01

99

Combined feedback-feedforward active noise-reducing headset--The effect of the acoustics on broadband performance  

NASA Astrophysics Data System (ADS)

Active noise-reducing headsets that employ analog feedback control and provide good broadband attenuation are commercially available for a wide range of applications. Recent studies have explored the integration of an adaptive digital feedforward controller with the analog feedback controller to provide additional attenuation of periodic noise components. This paper presents an experimental study of such a combined control system, but with both feedback- and feedforward controllers attenuating broadband noise. Good performance is demonstrated in a reverberant sound field, while under direct sound-field conditions the attenuation performance of the feedforward controller is shown to be dependent on head position. The paper concludes with an analysis of the forward path delay showing how the passive attenuation mechanism improves broadband performance. copyright 2002 Acoustical Society of America.

Rafaely, Boaz; Jones, Matthew

2002-09-01

100

Noise Prediction Module for Offset Stream Nozzles  

NASA Technical Reports Server (NTRS)

A Modern Design of Experiments (MDOE) analysis of data acquired for an offset stream technology was presented. The data acquisition and concept development were funded under a Supersonics NRA NNX07AC62A awarded to Dimitri Papamoschou at University of California, Irvine. The technology involved the introduction of airfoils in the fan stream of a bypass ratio (BPR) two nozzle system operated at transonic exhaust speeds. The vanes deflected the fan stream relative to the core stream and resulted in reduced sideline noise for polar angles in the peak jet noise direction. Noise prediction models were developed for a range of vane configurations. The models interface with an existing ANOPP module and can be used or future system level studies.

Henderson, Brenda S.

2011-01-01

101

23 CFR 772.17 - Traffic noise prediction.  

Code of Federal Regulations, 2011 CFR

...as provided in 49 CFR part 7. These documents are also available on the FHWA's Traffic Noise Model Web site at the following URL: http://www.trafficnoisemodel.org/main.html. (b) In predicting noise levels and assessing noise...

2011-04-01

102

23 CFR 772.17 - Traffic noise prediction.  

Code of Federal Regulations, 2010 CFR

...as provided in 49 CFR part 7. These documents are also available on the FHWA's Traffic Noise Model Web site at the following URL: http://www.trafficnoisemodel.org/main.html. (b) In predicting noise levels and assessing noise...

2010-04-01

103

Jet noise prediction using different turbulent scales  

NASA Astrophysics Data System (ADS)

The turbulent energy dissipation rate time-scale and length-scale has been routinely used for the prediction of noise from turbulent flows, particularly jet streams. However, this is not the only possible choice. In general, scales evolving in a turbulent medium are threefold. First, those associated with the mean flow; second, those attributed to the turbulence and the mean flow interactions; and third, scales related to the turbulence-turbulence interactions. In this paper, special attention will be paid to further study of the underlying physics of aerodynamic noise by examining various time-scales. To do so, three time scales, namely, dissipation, production, and strain rate time scales, are defined and used in the source modelling to emphasis the effect of the turbulence structures at different jet regions on the jet noise production mechanism. The required mean value and turbulence parameters are obtained using a modified k - ? turbulence model, and Lighthill’s Acoustic Analogy is used for the prediction of the emanated noise.

Self, Rod H.; Azarpeyvand, Mahdi

2009-05-01

104

Initial noise predictions for rudimentary landing gear  

NASA Astrophysics Data System (ADS)

A four-wheel "rudimentary" landing gear (RLG) truck was designed for public-domain research, with a level of complexity which is manageable in current numerical simulations, and a weak Reynolds-number sensitivity. Experimental measurements of wall-pressure fluctuations are allowing a meaningful test of unsteady simulations with emphasis on noise generation. We present three Detached-Eddy Simulations (DES) using up to 18 million points in the high-order NTS code. The first is incompressible with the model placed in the wind tunnel, as requested for the 2010 workshop on Benchmark problems for Airframe Noise Computations (BANC-I), intended for force and surface-pressure studies. The second and third are at Mach 0.115 and Mach 0.23, with only one wall, a "ceiling" analogous to a wing (but infinite and inviscid), and are used to exercise far-field noise prediction by coupling the Detached-Eddy Simulations and a Ffowcs-Williams/Hawkings calculation. The results include wall-pressure, and far-field-noise intensities and spectra. The wall pressure signals in the three simulations are very similar and, in a comparison published separately, agree well with experiment and other simulations. In the absence of experimental noise data, the attention is focused on internal quality checks, by varying the permeable Ffowcs-Williams/Hawkings calculation surface and then by using only the solid surface. An unexpected finding at these Mach numbers is an apparent strong role for quadrupoles, revealed by a typical deficit of 3 dB in the solid-surface results, relative to the permeable-surface results. The solid-surface approach has variants, related to the presence of the ceiling (a plane of symmetry), which can increase this error further; there is little consensus on the exact configuration of the solid surfaces in the Ffowcs-Williams/Hawkings calculation procedure. Tentative theoretical arguments suggest that a balance somewhat in favor of quadrupoles over dipoles is plausible at Mach 0.115. However, the scaling of sound with Mach number does not follow the eighth power, as quadrupoles do in theory: it is closer to the sixth power. This trend gives a muddled theoretical picture, but agrees with the scaling observed in experiments. If it is confirmed, this finding will complicate airframe-noise calculations, and prevent the attribution of noise to a given component of the aircraft. Progress in airframe-noise simulations appears real, but systematic grid-refinement studies and noise comparisons with experiment or other simulations have yet to occur, and the theoretical uncertainty is high.

Spalart, Philippe R.; Shur, Mikhail L.; Strelets, Mikhail Kh.; Travin, Andrey K.

2011-08-01

105

Comparison of predicted engine core noise with current and proposed aircraft noise certification requirements  

NASA Technical Reports Server (NTRS)

Predicted engine core noise levels are compared with measured total aircraft noise levels and with current and proposed federal noise certification requirements. Comparisons are made at the FAR-36 measuring stations and include consideration of both full- and cutback-power operation at takeoff. In general, core noise provides a barrier to achieving proposed EPA stage 5 noise levels for all types of aircraft. More specifically, core noise levels will limit further reductions in aircraft noise levels for current widebody commercial aircraft.

Vonglahn, U. H.; Groesbeck, D. E.

1981-01-01

106

Interior noise prediction methodology: ATDAC theory and validation  

NASA Astrophysics Data System (ADS)

The Acoustical Theory for Design of Aircraft Cabins (ATDAC) is a computer program developed to predict interior noise levels inside aircraft and to evaluate the effects of different aircraft configurations on the aircraft acoustical environment. The primary motivation for development of this program is the special interior noise problems associated with advanced turboprop (ATP) aircraft where there is a tonal, low frequency noise problem. Prediction of interior noise levels requires knowledge of the energy sources, the transmission paths, and the relationship between the energy variable and the sound pressure level. The energy sources include engine noise, both airborne and structure-borne; turbulent boundary layer noise; and interior noise sources such as air conditioner noise and auxiliary power unit noise. Since propeller and engine noise prediction programs are widely available, they are not included in ATDAC. Airborne engine noise from any prediction or measurement may be input to this program. This report describes the theory and equations implemented in the ATDAC program.

Mathur, Gopal P.; Gardner, Bryce K.

1992-04-01

107

A rod-airfoil experiment as a benchmark for broadband noise modeling  

NASA Astrophysics Data System (ADS)

A low Mach number rod-airfoil experiment is shown to be a good benchmark for numerical and theoretical broadband noise modeling. The benchmarking approach is applied to a sound computation from a 2D unsteady-Reynolds-averaged Navier Stokes (U-RANS) flow field, where 3D effects are partially compensated for by a spanwise statistical model and by a 3D large eddy simulation. The experiment was conducted in the large anechoic wind tunnel of the Ecole Centrale de Lyon. Measurements taken included particle image velocity (PIV) around the airfoil, single hot wire, wall pressure coherence, and far field pressure. These measurements highlight the strong 3D effects responsible for spectral broadening around the rod vortex shedding frequency in the subcritical regime, and the dominance of the noise generated around the airfoil leading edge. The benchmarking approach is illustrated by two examples: the validation of a stochastical noise generation model applied to a 2D U-RANS computation;

Jacob, Marc C.; Boudet, Jérôme; Casalino, Damiano; Michard, Marc

2005-07-01

108

New approach to time domain classification of broadband noise in gravitational wave data  

NASA Astrophysics Data System (ADS)

Transient broadband noise in gravitational wave (GW) detectors—also known as noise triggers (referred to as triggers for brevity)—can often be a deterrant to the efficiency with which astrophysical search pipelines detect sources. It is important to understand their instrumental or environmental origin so that they could be eliminated or accounted for in the data. Since the number of triggers is large, data mining approaches such as clustering and classification are useful tools for this task. Classification of triggers based on a handful of discrete properties has been done in the past. A rich information content is available in the waveform or “shape” of the triggers that has had a rather restricted exploration so far. This paper presents a new way to classify triggers deriving information from both trigger waveforms as well as their discrete physical properties, using a sequential combination of the longest common subsequence (LCSS) and LCSS coupled with Fast Time Series Evaluation (FTSE) for waveform classification, and the multidimensional hierarchical classification (MHC) analysis for the grouping based on physical properties. A generalized k-means algorithm is used with the LCSS (and LCSS+FTSE) for clustering the triggers using a validity measure to determine the correct number of clusters in absence of any prior knowledge. The results have been demonstrated by simulations and by application to a segment of real LIGO data from the sixth science run.

Mukherjee, S.; Rizwan, P.; Biswas, R.

2012-07-01

109

Prediction of Jet Noise Shielding with Forward Flight Salvador Mayoral  

E-print Network

Prediction of Jet Noise Shielding with Forward Flight Effects Salvador Mayoral and Dimitri source, simulating jet noise, from a surface having the general shape of the hybrid-wing-body (HWB of propulsion noise sources by the airframe. The focus of this study is the diffraction of a wavepacket noise

Papamoschou, Dimitri

110

The Acoustic Analogy and Alternative Theories for Jet Noise Prediction  

Microsoft Academic Search

This paper describes several methods for the prediction of jet noise. All but one of the noise prediction schemes are based on Lighthill's or Lilley's acoustic analogy while the other is the jet noise generation model recently proposed by Tam and Auriault. In all the approaches some assumptions must be made concerning the statistical properties of the turbulent sources. In

Philip J. Morris; F. Farassat

2002-01-01

111

Observations of correlated broadband electrostatic noise and electron-cyclotron emissions in the plasma sheet. Technical report  

SciTech Connect

Electric field wave observations in the central plasma sheet of the earth's magnetosphere show the correlated occurrence of broadband electrostatic noise and electrostatic electron cyclotron harmonic emissions. A model is proposed in which the broadband emissions are electron acoustic waves generated by an observed low energy electron beam, and the cyclotron emissions are generated by the hot electron loss cone instability. The high degree of correlation between the two emissions is provided in the model by the presence of the cold electron beam population, which allows both of the plasma instabilities to grow.

Roeder, J.L.; Angelopoulos, V.; Baumjohann, W.; Anderson, R.R.

1991-11-15

112

Near real-time noise removal for the Monterey Ocean Bottom Broadband (MOBB) seismic station data  

NASA Astrophysics Data System (ADS)

The Monterey Ocean Bottom Broadband (MOBB) observatory, located 40 km offshore central California, at a water depth of 1000 m, provides important complementary coverage of the San Andreas Fualt system to the land-based network. First installed in 2002, it is arguably the longest lived ocean bottom broadband seismic station. It includes a three-component broadband Guralp CMG-1T seismometer and a collocated differential pressure gauge (DPG) to measure the local water pressure continuously, as well as a current meter. After 7 years of autonomous operation, in February 2009, MOBB was successfully connected to the MARS cable (http://www.mbari.org/mars), and the data have been available in real time at the Northern California Earthquake Data Center (Romanowicz et al., 2009). However, the usage of MOBB data has been limited because of the noisy character of the data, in particular at periods of interest for regional moment tensor studies (20-100 sec), due to the ocean infragravity waves. Crawford and Webb (2000) demonstrated that there is a strong correlation between the water pressure and the vertical component of seafloor ground velocity in the infragravity wave band. Applying this to MOBB vertical component data, a transfer function (TF) was determined and utilized to successfully deconvolve the pressure-correlated noise from the vertical component of MOBB seismograms (Dolenc et al., 2007) in the period band 20-200 sec. Romanowicz et al. (2003, 2009) presented examples of how the cleaned MOBB data contribute to the determination of source parameters and regional structure. These past efforts, however, have been mostly case studies for illustration purpose. In this study, we systematically process all the available MOBB data since 2009 (because the cable was trawled, about a year of data is missing from February 2010 to June 2011). We calculate the TF over time and find that it is generally very stable, except for one change in 2010 due to an instrument replacement. Two universal TF's (one for the period before the change and one after) are therefore defined and utilized for systematic noise removal. We demonstrate the effectiveness of the technique by applying the cleaned MOBB data to moment tensor inversion of all Mw4.0+ and many Mw 3.5+ events in Northern and Central California in 2009-2012. In addition, we also try to process the MOBB data before 2009. Although the TF is less coherent during the autonomous period of operation due to various problems with one or the other of the instruments, there is potential for application to at least part of the data. Because the vertical component TF is so stable, it can be computed in advance, and the noise removal can be done routinely in near real-time ( with ~8 minutes delay), which is sufficient for routine regional moment tensor determination. This procedure is in the process of implementation in the northern California real time earthquake notification system.

Guinois, M.; Zheng, Z.; Taira, T.; Romanowicz, B. A.

2012-12-01

113

Noise performance of IRIS/IDA broadband seismic stations AAK and TLY in the USSR. Semi-Annual technical report  

SciTech Connect

Averaged ambient ground noise power spectra are found two broadband IRIS/IDA seismic stations deployed at Talaya (TLY) near Lake Baikal in Russia and Ala-Archa (AAK) near Bishkek in Kirghizia, central Asia. Site descriptions are also provided for these two stations, as well as major episodes up to mid 1991 in their operational history that are relevant to potential data users. Findings can be summarized as follows: AAK shows among the lowest average absolute nighttime noise levels above I Hz documented to date for IRIS/IDA stations in the former USSR; its night-averaged noise levels above 1 Hz are very similar to those observed at GAR. Ground noise increases during the day over night levels at AAK, with the maximum increase (7-9 dB) occurring between 2-3 Hz. Below .7 Hz, day and night noise levels are the same at AAK. TLY average nighttime ground noise levels are about 6- 1 0 dB higher than AAK levels above 1 Hz; its night-averaged noise levels above 1 Hz are very similar to those observed at IRIS/IDA station KIV. Below .6 Hz, nighttime levels at AAK and TLY are comparable, except that TLY has lower horizontal noise levels (4-5 dB) at periods longer than 25 s. Almost no difference between night and day noise levels was observed at TLY; in this sense it is unique among the IRIS/IDA broadband stations in the USSR. microseism peaks at both stations are comparable (between - 135 to - 140 dB relative to (1 m/s2)2/Hz) at both stations. High-frequency noise levels appear to be fairly constant between 10 - 50 Hz, at between - 150 to - 140 dB relative to (I m/s2)2/Hz.

Given, H.K.

1992-01-15

114

Coherence and Phase Relationships of Broadband Ambient Seismic Noise in the Pacific Ocean  

NASA Astrophysics Data System (ADS)

The persistence and spectral variation of coherence between the pressure and vertical particle velocity of the broadband ambient seismic noise field in the North Pacific reflects both local and remote climate-induced ocean gravity wave variability. The noise spectrum is forced by four ocean gravity wave mechanisms in separate frequency bands: (a) infragravity (IG) waves [< 0.04] Hz, (b) primary microseisms (PM) [0.04, 0.085] Hz, (c) double frequency (DF) microseisms [0.085, ~6-7] Hz, and (d) acoustic noise from breaking waves [> 7] Hz. The Hawaii-2 Observatory (H2O) and the Ocean Seismic Network Pilot Experiment (OSNPE) data each show a distinct and systematic banding pattern in the coherence between pressure and vertical velocity. This banding generally does not correspond to peaks in either the pressure or velocity spectra, which have been associated with sediment shear wave resonances (Scholte modes), a common feature in ambient noise records. The magnitude and phase of this coherence are useful tools for identifying primary (PM) and double frequency (DF) microseism energy that has been generated at distant coastlines by direct loading in shallow water and wave-wave interaction, respectively. Furthermore it is possible that coherence/phase relationships can be used to distinguish DF microseisms generated near coastlines from DF microseisms generated in the open ocean. Time-domain finite-difference modeling can be used to study the phase coherence for complex models involving Rayleigh waves, pseudo-Rayleigh waves, Scholte (Stoneley) waves and higher order modes (resonances). As an example, for an unsedimented seafloor (just an ocean layer over igneous crust, with suitable velocity gradients in each, over a bandwidth of 7-13Hz), model data show only a single interface wave, the fundamental Scholte mode, for which the vertical velocity is 90 degrees out of phase with the pressure. In contrast, adding a 25m thick soft sediment layer introduces a family of higher order modes with a number of the characteristics that much more closely resemble those observed in ocean bottom data: i) the relative contributions of pressure and particle velocities vary substantially between modes, ii) phase shifts change continuously and gradually through strong and sudden changes in magnitude, and iii) phase shifts of 45 and 135 degrees are not uncommon.

Stephen, R. A.; Bromirski, P. D.

2008-12-01

115

Jet noise prediction using a sweeping based turbulence generation process  

E-print Network

Jet noise prediction using a sweeping based turbulence generation process A. Lafittea , E that these devices could contribute directly to ramp noise, the use of a numerical tool to predict acoustics of jet-27 April 2012, Nantes, France 1323 #12;A predictive tool for acoustics of confined subsonic jets

Paris-Sud XI, Université de

116

A broad-band MQW semiconductor optical amplifier with high saturation output power and low noise figure  

Microsoft Academic Search

A broad-band semiconductor optical amplifier (SOA) that achieves both a high chip saturation output power and a low chip noise figure (NF) was developed by using a thin multiquantum well with low internal loss. The SOA exhibited a high chip saturation output power of >+19.6 dBm and a low chip NF of <4.5 dB over a 3-dB gain bandwidth of

Ken Morito; Shinsuke Tanaka; Shuich Tomabechi; Akito Kuramata

2005-01-01

117

Aircraft system noise prediction: Past, present, and future  

NASA Astrophysics Data System (ADS)

Aircraft system noise prediction is necessary to estimate the community noise impact of future aircraft and to estimate the noise impacts of changes in propulsion systems, airframes, or operations of current aircraft. Aircraft system noise is the sum of noise generated by various components of the propulsion system and the various components of the airframe including the landing gear. Predicting noise on the ground from an aircraft flyover requires estimating the noise generated by the many contributing sources during the flyover as the flight conditions change, summing these sources as a function of time, and propagating the resultant combined source through the atmosphere to the observer location. NASA introduced the Aircraft Noise Prediction Program (ANOPP) about 30 years ago and continually upgraded and extended the code prediction capability. The history of ANOPP will be reviewed along with current efforts to make it more useful as a design tool. A proposed new systems prediction program, AVATAR, will be less empirical and capable of predicting community noise from unconventional aircraft planforms. Innovative/unconventional aircraft configurations will be required to meet aggressive noise goals in the future.

Golub, Robert A.; Posey, Joe W.

2003-04-01

118

The Broad-Band Seismic Noise Wavefield at the Larderello-Travale Geothermal Field (Italy)  

NASA Astrophysics Data System (ADS)

Cross-correlation of ambient noise wave-field between a pair of receivers (NCF), provides an estimate of the Green's Function between the two sites, thus allowing extraction of the associated group velocity dispersion curve. This is valid under the assumption that noise sources and/or scatterers are isotropically distributed and uncorrelated each other. These conditions are usually met once the cross-correlations are averaged over long time intervals. At frequencies lower than 1 Hz, ambient noise wavefield is essentially composed by surface waves that are mostly associated with oceanic sources; as a consequence, the noise wavefield may exhibit marked directional properties over short (day) to intermediate (weeks) time scales. A detailed assessment of the nature and duration of these sources is therefore required in order to define the optimal conditions for retrieving the Green's functions from NCF analysis. This study presents ambient noise analysis for the Larderello-Travale Geothermal Field (Italy). We use data collected by a temporary seismic array consisting of 20 broad-band instruments, with station spacing ranging from 6 to 50 Km. Below 1 Hz, the most energetic sources are those associated with both primary and secondary microseisms, with dominant spectral peaks spanning the 0.05-0.5 Hz frequency range. Focusing on the secondary microseism sources (f > 0.1 Hz), we test the validity of the isotropic-wavefield assumption by determining the kinematic properties of the wavefield using frequency-domain beamforming. For the May-November 2012 time span, our results show that the most energetic and persistent wavefield components propagate from WNW (Gulf of Marseille and Genova) and SW (Sardinia channel). In the late part of the observation period, additional wavefield components are observed to propagate from the NE-SE azimuthal range, corresponding to sources located throughout the Adriatic sea. This suggests that the conditions for the application of the NCF technique can be met by averaging cross-correlation estimates over a period of a few months. The NCF analysis included a pre-processing step, consisting of signal filtering and normalization. Then, we calculated cross-correlations between all independent station pairs, and stacked these functions over the entire observation period. Finally, the retrieved Green's functions are subjected to a frequency-time analysis, in order to obtain group velocity dispersion curves for each station pair. The local velocity structure and the inter-station distances are key factors conditioning the frequency range within which the surface wave dispersion can be correctly measured. When the ratio between the inter-station distance and the wavelength of interest is lower than ~3, NCF can severely fail. For these cases, we used the Spatial Autocorrelation Function (SPAC), which relates the frequency-dependent spatial autocorrelation functions to the phase velocity dispersion curve. In the analyzed frequency band we also found evidences for signals traveling with high apparent velocities ( > 8000 m/s). Beamforming and polarization analysis indicate that these signals are likely associated with P-waves generated in deep water far from coastlines.

Zupo, M.; Saccorotti, G.; Piccinini, D.

2013-12-01

119

Prediction of Landing Gear Noise Reduction and Comparison to Measurements  

NASA Technical Reports Server (NTRS)

Noise continues to be an ongoing problem for existing aircraft in flight and is projected to be a concern for next generation designs. During landing, when the engines are operating at reduced power, the noise from the airframe, of which landing gear noise is an important part, is equal to the engine noise. There are several methods of predicting landing gear noise, but none have been applied to predict the change in noise due to a change in landing gear design. The current effort uses the Landing Gear Model and Acoustic Prediction (LGMAP) code, developed at The Pennsylvania State University to predict the noise from landing gear. These predictions include the influence of noise reduction concepts on the landing gear noise. LGMAP is compared to wind tunnel experiments of a 6.3%-scale Boeing 777 main gear performed in the Quiet Flow Facility (QFF) at NASA Langley. The geometries tested in the QFF include the landing gear with and without a toboggan fairing and the door. It is shown that LGMAP is able to predict the noise directives and spectra from the model-scale test for the baseline configuration as accurately as current gear prediction methods. However, LGMAP is also able to predict the difference in noise caused by the toboggan fairing and by removing the landing gear door. LGMAP is also compared to far-field ground-based flush-mounted microphone measurements from the 2005 Quiet Technology Demonstrator 2 (QTD 2) flight test. These comparisons include a Boeing 777-300ER with and without a toboggan fairing that demonstrate that LGMAP can be applied to full-scale flyover measurements. LGMAP predictions of the noise generated by the nose gear on the main gear measurements are also shown.

Lopes, Leonard V.

2010-01-01

120

Features in the broad-band eclipse spectra of exoplanets: signal or noise?  

NASA Astrophysics Data System (ADS)

A planet's emission spectrum contains information about atmospheric composition and structure. We compare the Bayesian Information Criterion (BIC) of blackbody fits and idealized spectral retrieval fits for the 44 planets with published eclipse measurements in multiple thermal wavebands, mostly obtained with the Spitzer Space Telescope. The evidence for spectral features depends on eclipse depth uncertainties. Spitzer has proven capable of eclipse precisions better than 10-4 when multiple eclipses are analysed simultaneously, but this feat has only been performed four times. It is harder to self-calibrate photometry when a single occultation is reduced and analysed in isolation; we find that such measurements have not passed the test of repeatability. Single-eclipse measurements either have an uncertainty floor of 5 × 10-4, or their uncertainties have been underestimated by a factor of 3. If one adopts these empirical uncertainties for single-eclipse measurements, then the evidence for molecular features all but disappears: blackbodies have better BIC than spectral retrieval for all planets, save HD 189733b, and the few planets poorly fit by blackbodies are also poorly fit by self-consistent radiative transfer models. This suggests that the features in extant broad-band emission spectra are due to astrophysical and instrumental noise rather than molecular bands. Claims of stratospheric inversions, disequilibrium chemistry, and high C/O ratios based solely on photometry are premature. We recommend that observers be cautious of error estimates from self-calibration of small data sets, and that modellers compare the evidence for spectral models to that of simpler models such as blackbodies.

Hansen, Christopher J.; Schwartz, Joel C.; Cowan, Nicolas B.

2014-11-01

121

Passive geoacoustic inversion with a single hydrophone using broadband ship noise.  

PubMed

An inversion scheme is proposed, relying upon the inversion of the noise of a moving ship measured on a single distant hydrophone. The spectrogram of the measurements exhibits striations which depend on waveguide parameters. The periodic behavior of striations versus range are used to estimate the differences of radial wavenumber between couples of propagative modes at a given frequency. These wavenumber differences are stacked for several frequencies to form the relative dispersion curves. Such relative dispersion curves can be synthesized using a propagation model feeded with a bottom geoacoustic model. Inversion is performed by looking for the bottom properties that optimize the fit between measured and predicted relative dispersion curves. The inversion scheme is tested on simulated data. The conclusions are twofold: (1) a minimum 6 dB signal to noise ratio is required to obtained an unbiased estimate of compressional sound speed in the bottom with a 3 m s(-1) standard deviation; however, even with low signal to noise ratio, the estimation error remains bounded and (2) in the case of a multi-layer bottom, the scheme produces a single depth-average compressional sound speed. The inversion scheme is applied on experimental data. The results are fully consistent with a core sample measured around the receiving hydrophone. PMID:22423697

Gervaise, C; Kinda, B G; Bonnel, J; Stéphan, Y; Vallez, S

2012-03-01

122

Modular Engine Noise Component Prediction System (MCP) Technical Description and Assessment Document  

NASA Technical Reports Server (NTRS)

This report describes an empirical prediction procedure for turbofan engine noise. The procedure generates predicted noise levels for several noise components, including inlet- and aft-radiated fan noise, and jet-mixing noise. This report discusses the noise source mechanisms, the development of the prediction procedures, and the assessment of the accuracy of these predictions. Finally, some recommendations for future work are presented.

Herkes, William H.; Reed, David H.

2005-01-01

123

Experimental validation of boundary element methods for noise prediction  

NASA Technical Reports Server (NTRS)

Experimental validation of methods to predict radiated noise is presented. A combined finite element and boundary element model was used to predict the vibration and noise of a rectangular box excited by a mechanical shaker. The predicted noise was compared to sound power measured by the acoustic intensity method. Inaccuracies in the finite element model shifted the resonance frequencies by about 5 percent. The predicted and measured sound power levels agree within about 2.5 dB. In a second experiment, measured vibration data was used with a boundary element model to predict noise radiation from the top of an operating gearbox. The predicted and measured sound power for the gearbox agree within about 3 dB.

Seybert, A. F.; Oswald, Fred B.

1992-01-01

124

Modular Engine Noise Component Prediction System (MCP) Program Users' Guide  

NASA Technical Reports Server (NTRS)

This is a user's manual for Modular Engine Noise Component Prediction System (MCP). This computer code allows the user to predict turbofan engine noise estimates. The program is based on an empirical procedure that has evolved over many years at The Boeing Company. The data used to develop the procedure include both full-scale engine data and small-scale model data, and include testing done by Boeing, by the engine manufacturers, and by NASA. In order to generate a noise estimate, the user specifies the appropriate engine properties (including both geometry and performance parameters), the microphone locations, the atmospheric conditions, and certain data processing options. The version of the program described here allows the user to predict three components: inlet-radiated fan noise, aft-radiated fan noise, and jet noise. MCP predicts one-third octave band noise levels over the frequency range of 50 to 10,000 Hertz. It also calculates overall sound pressure levels and certain subjective noise metrics (e.g., perceived noise levels).

Golub, Robert A. (Technical Monitor); Herkes, William H.; Reed, David H.

2004-01-01

125

Aircraft cabin noise prediction and optimization  

NASA Technical Reports Server (NTRS)

Theoretical and experimental studies were conducted to determine the noise transmission into acoustic enclosures ranging from simple rectangular box models to full scale light aircraft in flight. The structural models include simple, stiffened, curved stiffened, and orthotropic panels and double wall windows. The theoretical solutions were obtained by model analysis. Transfer matrix and finite element procedures were utilized. Good agreement between theory and experiment has been achieved. An efficient acoustic add-on treatment was developed for interior noise control in a twin engine light aircraft.

Vaicaitis, R.

1985-01-01

126

Interior noise prediction methodology: ATDAC theory and validation  

Microsoft Academic Search

The Acoustical Theory for Design of Aircraft Cabins (ATDAC) is a computer program developed to predict interior noise levels inside aircraft and to evaluate the effects of different aircraft configurations on the aircraft acoustical environment. The primary motivation for development of this program is the special interior noise problems associated with advanced turboprop (ATP) aircraft where there is a tonal,

Gopal P. Mathur; Bryce K. Gardner

1992-01-01

127

The interim prediction for aircraft noise  

Microsoft Academic Search

The acoustic emission from an aircraft during the flight is a dynamic process. The emitting acoustic power and received mean square acoustic pressure are the function of time. The paper deals with this problem as a quasi-steady one. The whole process is resolved into several elementary procedures, for example, the flight trajectory, the geometric relation between the noise sources and

Diyi Tang; Wenlan Li; Weiyang Qiao; Zhenxia Liu

1990-01-01

128

Study on Noise Prediction Model and Control Schemes for Substation  

PubMed Central

With the government's emphasis on environmental issues of power transmission and transformation project, noise pollution has become a prominent problem now. The noise from the working transformer, reactor, and other electrical equipment in the substation will bring negative effect to the ambient environment. This paper focuses on using acoustic software for the simulation and calculation method to control substation noise. According to the characteristics of the substation noise and the techniques of noise reduction, a substation's acoustic field model was established with the SoundPLAN software to predict the scope of substation noise. On this basis, 4 reasonable noise control schemes were advanced to provide some helpful references for noise control during the new substation's design and construction process. And the feasibility and application effect of these control schemes can be verified by using the method of simulation modeling. The simulation results show that the substation always has the problem of excessive noise at boundary under the conventional measures. The excess noise can be efficiently reduced by taking the corresponding noise reduction methods. PMID:24672356

Gao, Yang; Liu, Songtao

2014-01-01

129

Study on noise prediction model and control schemes for substation.  

PubMed

With the government's emphasis on environmental issues of power transmission and transformation project, noise pollution has become a prominent problem now. The noise from the working transformer, reactor, and other electrical equipment in the substation will bring negative effect to the ambient environment. This paper focuses on using acoustic software for the simulation and calculation method to control substation noise. According to the characteristics of the substation noise and the techniques of noise reduction, a substation's acoustic field model was established with the SoundPLAN software to predict the scope of substation noise. On this basis, 4 reasonable noise control schemes were advanced to provide some helpful references for noise control during the new substation's design and construction process. And the feasibility and application effect of these control schemes can be verified by using the method of simulation modeling. The simulation results show that the substation always has the problem of excessive noise at boundary under the conventional measures. The excess noise can be efficiently reduced by taking the corresponding noise reduction methods. PMID:24672356

Chen, Chuanmin; Gao, Yang; Liu, Songtao

2014-01-01

130

Initial Integration of Noise Prediction Tools for Acoustic Scattering Effects  

NASA Technical Reports Server (NTRS)

This effort provides an initial glimpse at NASA capabilities available in predicting the scattering of fan noise from a non-conventional aircraft configuration. The Aircraft NOise Prediction Program, Fast Scattering Code, and the Rotorcraft Noise Model were coupled to provide increased fidelity models of scattering effects on engine fan noise sources. The integration of these codes led to the identification of several keys issues entailed in applying such multi-fidelity approaches. In particular, for prediction at noise certification points, the inclusion of distributed sources leads to complications with the source semi-sphere approach. Computational resource requirements limit the use of the higher fidelity scattering code to predict radiated sound pressure levels for full scale configurations at relevant frequencies. And, the ability to more accurately represent complex shielding surfaces in current lower fidelity models is necessary for general application to scattering predictions. This initial step in determining the potential benefits/costs of these new methods over the existing capabilities illustrates a number of the issues that must be addressed in the development of next generation aircraft system noise prediction tools.

Nark, Douglas M.; Burley, Casey L.; Tinetti, Ana; Rawls, John W.

2008-01-01

131

Processing seismic ambient noise data to obtain reliable broad-band surface wave dispersion measurements  

Microsoft Academic Search

SUMMARY Ambient noise tomography is a rapidly emerging field of seismological research. This paper presents the current status of ambient noise data processing as it has developed over the past several years and is intended to explain and justify this development through salient examples. The ambient noise data processing procedure divides into four principal phases: (1) single station data preparation,

G. D. Bensen; M. H. Ritzwoller; M. P. Barmin; A. L. Levshin; F. Lin; M. P. Moschetti; N. M. Shapiro; Y. Yang

2007-01-01

132

Measured and predicted noise of the Avco-Lycoming YF-102 turbofan noise  

NASA Technical Reports Server (NTRS)

Acoustic testing of the AVCO-Lycoming YF-102 turbofan engine was done on a static test stand in support of the quiet short-haul research aircraft acoustic design. Overall noise levels were dominated by the fan noise emanating from the exhaust duct, except at high power settings when combination tones were generated in the fan inlet. Component noise levels, calculated by noise prediction methods were in reasonable agreement with the measured results. Far-field microphones placed at ground level were found superior to those at engine centerline height, even at high frequencies.

Clark, B. J.; Mcardle, J. G.; Homyak, L.

1979-01-01

133

Increased Fidelity in Prediction Methods For Landing Gear Noise  

NASA Technical Reports Server (NTRS)

An aeroacoustic prediction scheme has been developed for landing gear noise. The method is designed to handle the complex landing gear geometry of current and future aircraft. The gear is represented by a collection of subassemblies and simple components that are modeled using acoustic elements. These acoustic elements are generic, but generate noise representative of the physical components on a landing gear. The method sums the noise radiation from each component of the undercarriage in isolation accounting for interference with adjacent components through an estimate of the local upstream and downstream flows and turbulence intensities. The acoustic calculations are made in the code LGMAP, which computes the sound pressure levels at various observer locations. The method can calculate the noise from the undercarriage in isolation or installed on an aircraft for both main and nose landing gear. Comparisons with wind tunnel and flight data are used to initially calibrate the method, then it may be used to predict the noise of any landing gear. In this paper, noise predictions are compared with wind tunnel data for model landing gears of various scales and levels of fidelity, as well as with flight data on fullscale undercarriages. The present agreement between the calculations and measurements suggests the method has promise for future application in the prediction of airframe noise.

Lopes, Leonard V.; Brentner, Kenneth S.; Morris, Philip J.; Lockhard, David P.

2006-01-01

134

A Hybrid RANS/LES Approach for Predicting Jet Noise  

NASA Technical Reports Server (NTRS)

Hybrid acoustic prediction methods have an important advantage over the current Reynolds averaged Navier-Stokes (RANS) based methods in that they only involve modeling of the relatively universal subscale motion and not the configuration dependent larger scale turbulence. Unfortunately, they are unable to account for the high frequency sound generated by the turbulence in the initial mixing layers. This paper introduces an alternative approach that directly calculates the sound from a hybrid RANS/LES flow model (which can resolve the steep gradients in the initial mixing layers near the nozzle lip) and adopts modeling techniques similar to those used in current RANS based noise prediction methods to determine the unknown sources in the equations for the remaining unresolved components of the sound field. The resulting prediction method would then be intermediate between the current noise prediction codes and previously proposed hybrid noise prediction methods.

Goldstein, Marvin E.

2006-01-01

135

Noise and chaos contributions in fast random bit sequence generated from broadband optoelectronic entropy sources  

E-print Network

quality obtained from this method, can be interpreted as a complex mixing operated on the initial analogue generation found a deep interest within the community of ana- logue broadband chaotic optical systems on analysis and experiments of their method, which leads to the discussion about the actual origin

Paris-Sud XI, Université de

136

PROGRESS TOWARD BROAD-BAND AMBIENT NOISE TOMOGRAPHY IN EURASIA Michael H. Ritzwoller1  

E-print Network

applications. The data are taken from about 125 broad-band seismic stations from the Global Seismic Network periods of 10 sec - 50 sec, respectively. Group speed maps at periods from 8 sec to 40 sec are estimated, and the resulting path coverage is denser and displays a more uniform azimuthal distribution than from earthquake

Ritzwolle, Mike

137

State of Jet Noise Prediction-NASA Perspective  

NASA Technical Reports Server (NTRS)

This presentation covers work primarily done under the Airport Noise Technical Challenge portion of the Supersonics Project in the Fundamental Aeronautics Program. To provide motivation and context, the presentation starts with a brief overview of the Airport Noise Technical Challenge. It then covers the state of NASA s jet noise prediction tools in empirical, RANS-based, and time-resolved categories. The empirical tools, requires seconds to provide a prediction of noise spectral directivity with an accuracy of a few dB, but only for axisymmetric configurations. The RANS-based tools are able to discern the impact of three-dimensional features, but are currently deficient in predicting noise from heated jets and jets with high speed and require hours to produce their prediction. The time-resolved codes are capable of predicting resonances and other time-dependent phenomena, but are very immature, requiring months to deliver predictions without unknown accuracies and dependabilities. In toto, however, when one considers the progress being made it appears that aeroacoustic prediction tools are soon to approach the level of sophistication and accuracy of aerodynamic engineering tools.

Bridges, James E.

2008-01-01

138

Acoustic Analogy and Alternative Theories for Jet Noise Prediction  

NASA Technical Reports Server (NTRS)

Several methods for the prediction of jet noise are described. All but one of the noise prediction schemes are based on Lighthill's or Lilley's acoustic analogy, whereas the other is the jet noise generation model recently proposed by Tam and Auriault. In all of the approaches, some assumptions must be made concerning the statistical properties of the turbulent sources. In each case the characteristic scales of the turbulence are obtained from a solution of the Reynolds-averaged Navier-Stokes equation using a kappa-sigma turbulence model. It is shown that, for the same level of empiricism, Tam and Auriault's model yields better agreement with experimental noise measurements than the acoustic analogy. It is then shown that this result is not because of some fundamental flaw in the acoustic analogy approach, but instead is associated with the assumptions made in the approximation of the turbulent source statistics. If consistent assumptions are made, both the acoustic analogy and Tam and Auriault's model yield identical noise predictions. In conclusion, a proposal is presented for an acoustic analogy that provides a clearer identification of the equivalent source mechanisms, as is a discussion of noise prediction issues that remain to be resolved.

Morris, Philip J.; Farassat, F.

2002-01-01

139

Stability Assessment and Quantitative Evaluation of H/ V Spectral Ratios for Site Response Studies in Kumaon Himalaya, India Using Ambient Noise Recorded by a Broadband Seismograph Network  

NASA Astrophysics Data System (ADS)

The Kumaon Himalaya region in India has accumulated considerable seismic risk potential from moderate to high seismicity due to ongoing tectonic evolutionary processes. To assess conditions of high seismic risk arising from local site effects at populated locations, we applied the empirical horizontal to vertical ( H/ V) spectral amplitude ratio method ( Nakamura in Quarterly Reports of the Railway Technical Research Institute Tokyo, 30:25-33, 1989) using ambient seismic noise recorded by a network of 32 digital broadband seismographs from June 2005 to June 2008. The data and the estimated parameters were subjected to stability tests to assess the effect of seasonal variations. Seasonal variations in the ambient noise data seemed to show a lesser effect on fundamental frequency estimates and a slightly greater effect on the peak H/ V amplitudes. Validation of the ambient noise results was done by complementary tests using H/ V ratios of local and regional earthquakes. The `peak' corresponding to the fundamental resonance frequency is prominently present in both the ambient noise and the earthquake datasets. The study locations showed distinct H/ V curve topologies, corresponding to the effects of both velocity contrast at well-defined frequencies and characteristic topographic effect around a certain frequency range. The clearly indicated `peaks' in the H/ V curves possibly correspond to velocity contrasts created by weathered sediments overlying hard rock basements in rocky hills. Our study indicates high site responses at many populated locations near the surface trace of the seismically active Main Central Thrust (MCT) and other fault boundaries. The fundamental resonance frequencies estimated from the site response studies at the 32 locations could be useful in preliminary site characterization, ground motion prediction and seismic hazard analysis.

Sivaram, K.; Mahesh, P.; Rai, S. S.

2012-10-01

140

Effects of broadband noise on cortical evoked auditory responses at different loudness levels in young adults.  

PubMed

Young adults with no history of hearing concerns were tested to investigate their /da/-evoked cortical auditory evoked potentials (P1-N1-P2) recorded from 32 scalp electrodes in the presence and absence of noise at three different loudness levels (soft, comfortable, and loud), at a fixed signal-to-noise ratio (+3 dB). P1 peak latency significantly increased at soft and loud levels, and N1 and P2 latencies increased at all three levels in the presence of noise, compared with the quiet condition. P1 amplitude was significantly larger in quiet than in noise conditions at the loudest level. N1 amplitude was larger in quiet than in noise for the soft level only. P2 amplitude was reduced in the presence of noise to a similar degree at all loudness levels. The differential effects of noise on P1, N1, and P2 suggest differences in auditory processes underlying these peaks. The combination of level and signal-to-noise ratio should be considered when using cortical auditory evoked potentials as an electrophysiological indicator of degraded speech processing. PMID:24323122

Sharma, Mridula; Purdy, Suzanne C; Munro, Kevin J; Sawaya, Kathleen; Peter, Varghese

2014-03-26

141

Predicting the responses of repetitively firing neurons to current noise.  

PubMed

We used phase resetting methods to predict firing patterns of rat subthalamic nucleus (STN) neurons when their rhythmic firing was densely perturbed by noise. We applied sequences of contiguous brief (0.5-2 ms) current pulses with amplitudes drawn from a Gaussian distribution (10-100 pA standard deviation) to autonomously firing STN neurons in slices. Current noise sequences increased the variability of spike times with little or no effect on the average firing rate. We measured the infinitesimal phase resetting curve (PRC) for each neuron using a noise-based method. A phase model consisting of only a firing rate and PRC was very accurate at predicting spike timing, accounting for more than 80% of spike time variance and reliably reproducing the spike-to-spike pattern of irregular firing. An approximation for the evolution of phase was used to predict the effect of firing rate and noise parameters on spike timing variability. It quantitatively predicted changes in variability of interspike intervals with variation in noise amplitude, pulse duration and firing rate over the normal range of STN spontaneous rates. When constant current was used to drive the cells to higher rates, the PRC was altered in size and shape and accurate predictions of the effects of noise relied on incorporating these changes into the prediction. Application of rate-neutral changes in conductance showed that changes in PRC shape arise from conductance changes known to accompany rate increases in STN neurons, rather than the rate increases themselves. Our results show that firing patterns of densely perturbed oscillators cannot readily be distinguished from those of neurons randomly excited to fire from the rest state. The spike timing of repetitively firing neurons may be quantitatively predicted from the input and their PRCs, even when they are so densely perturbed that they no longer fire rhythmically. PMID:24809636

Wilson, Charles J; Barraza, David; Troyer, Todd; Farries, Michael A

2014-05-01

142

Downwind rotor horizontal axis wind turbine noise prediction  

NASA Technical Reports Server (NTRS)

NASA and industry are currently cooperating in the conduct of extensive experimental and analytical studies to understand and predict the noise of large, horizontal axis wind turbines. This effort consists of (1) obtaining high quality noise data under well controlled and documented test conditions, (2) establishing the annoyance criteria for impulse noise of the type generated by horizontal axis wind turbines with rotors downwind of the support tower, (3) defining the wake characteristics downwind of the axial location of the plane of rotation, (4) comparing predictions with measurements made by use of wake data, and (5) comparing predictions with annoyance criteria. The status of work by Hamilton Standard in the above areas which was done in support of the cooperative NASA and industry studies is briefly summarized.

Metzger, F. B.; Klatte, R. J.

1981-01-01

143

Broad-band Gaussian noise is most effective in improving motor performance and is most pleasant  

PubMed Central

Modern attempts to improve human performance focus on stochastic resonance (SR). SR is a phenomenon in non-linear systems characterized by a response increase of the system induced by a particular level of input noise. Recently, we reported that an optimum level of 0–15 Hz Gaussian noise applied to the human index finger improved static isometric force compensation. A possible explanation was a better sensorimotor integration caused by increase in sensitivity of peripheral receptors and/or of internal SR. The present study in 10 subjects compares SR effects in the performance of the same motor task and on pleasantness, by applying three Gaussian noises chosen on the sensitivity of the fingertip receptors (0–15 Hz mostly for Merkel receptors, 250–300 Hz for Pacini corpuscles and 0–300 Hz for all). We document that only the 0–300 Hz noise induced SR effect during the transitory phase of the task. In contrast, the motor performance was improved during the stationary phase for all three noise frequency bandwidths. This improvement was stronger for 0–300 Hz and 250–300 Hz than for 0–15 Hz noise. Further, we found higher degree of pleasantness for 0–300 Hz and 250–300 Hz noise bandwidths than for 0–15 Hz. Thus, we show that the most appropriate Gaussian noise that could be used in haptic gloves is the 0–300 Hz, as it improved motor performance during both stationary and transitory phases. In addition, this noise had the highest degree of pleasantness and thus reveals that the glabrous skin can also forward pleasant sensations. PMID:24550806

Trenado, Carlos; Mikulic, Areh; Manjarrez, Elias; Mendez-Balbuena, Ignacio; Schulte-Monting, Jurgen; Huethe, Frank; Hepp-Reymond, Marie-Claude; Kristeva, Rumyana

2014-01-01

144

Simultaneous effects of sinusoidal whole body vibration and broadband noise on TTS 2 's and R-wave amplitudes in men at two different dry bulb temperatures  

Microsoft Academic Search

Summary The aim of this study was to investigate the temporary hearing threshold shift (TTS2) and R-wave amplitudes in eleven healthy males when they were exposed to paired sinusoidal whole body (Z-axis) vibration (5 Hz-2.12 m\\/s2) and stable broadband A-weighted white noise at dry bulb temperatures of 20°C and 30°C. The intensity of noise in the exposure combinations was 75,85

Olavi Manninen

1983-01-01

145

Bulletin of the Seismological Society of America, Vol. 95, No. 3, pp. 12021208, June 2005, doi: 10.1785/0120040098 Broadband Seismic Noise Analysis of the Himalayan Nepal Tibet  

E-print Network

, doi: 10.1785/0120040098 Broadband Seismic Noise Analysis of the Himalayan Nepal Tibet Seismic at sites to stabilize after deployment noise as part of the Himalayan Nepal Tibet Seismic Experiment (HIMNT seismometer deployed in Nepal and Tibet and then compared them with the high-noise model and low-noise Model

Sheehan, Anne F.

146

A comparative analysis of broadband and narrowband derived vegetation indices in predicting LAI and CCD of a cotton canopy  

NASA Astrophysics Data System (ADS)

Remote sensing is a powerful tool for obtaining important agronomic information about field crops. Many spectral vegetation indices (VIs) have been developed in the past three decades to provide more sensitive measurements of plant biophysical parameters and to reduce external noise interferences such as those related to soil and the atmosphere. Some VIs were developed based on narrowband spectral data and others on broadband sensors. Therefore, although the mathematical equations defining VIs are the same, their calculated values are different, thus affecting their stability in predicting agronomic variables such as total green leaf area index. The objective of this study was to compare the ability of VIs derived from broad and narrowbands and to determine the optimum red-NIR bands for VIs used in predicting leaf area index (LAI) and canopy chlorophyll density (CCD) of cotton canopies. A completely randomized experiment was conducted in a cotton ( Gossypium hirsutum L. cv. Sumian 3) field treated with four nitrogen application rates: 0%, 50%, 100% and 200% of the recommended rate. Hyperspectral reflectance was measured at 2.3 m above the cotton canopy on July 15, August 14 and October 1, 2002 using a FieldSpec® FR spectroradiometer. Corresponding leaf area index values and CCD were also measured on these dates. A large number (i.e. 22,500) of two-band combinations in the Normalized Difference Vegetation Index ( ?2 - ?1)/( ?1 + ?2) and the Ratio Vegetation index ?2/ ?1 was used for a linear and exponential regression analysis against LAI and CCD values. Moreover, traditional broadband vegetation indices based on simulated spectra were compared with their narrowband versions in predicting LAI and CCD. The results suggest that 640-660 nm and 800-870 nm, the centers of the red and NIR channels of several multi-spectral sensors on the current generation of earth-orbiting satellites, were not always the optimum wavelength position of red-NIR bands for VIs. Although different in formula, both the NDVI (normalized difference vegetation index) and RVI (ratio vegetation index) calculated from narrowbands at 690-710 nm and 750-900 nm were closely correlated with LAI ( R2 > 0.8) and CCD ( R2 > 0.85). The red-NIR band position was more important than band width for modeling LAI and CCD. In summary, hyperspectral remotely sensed data provide more alternative red-NIR bands compared to multi-spectral data and, therefore, can provide greater flexibility in predicting LAI and CCD.

Zhao, Dehua; Huang, Liangmei; Li, Jianlong; Qi, Jiaguo

147

A study of the prediction of cruise noise and laminar flow control noise criteria for subsonic air transports  

Microsoft Academic Search

General procedures for the prediction of component noise levels incident upon airframe surfaces during cruise are developed. Contributing noise sources are those associated with the propulsion system, the airframe and the laminar flow control (LFC) system. Transformation procedures from the best prediction base of each noise source to the transonic cruise condition are established. Two approaches to LFC\\/acoustic criteria are

G. Swift; P. Mungur

1979-01-01

148

Empirical source noise prediction method with application to subsonic coaxial jet mixing noise  

NASA Technical Reports Server (NTRS)

A general empirical method, developed for source noise predictions, uses tensor splines to represent the dependence of the acoustic field on frequency and direction and Taylor's series to represent the dependence on source state parameters. The method is applied to prediction of mixing noise from subsonic circular and coaxial jets. A noise data base of 1/3-octave-band sound pressure levels (SPL's) from 540 tests was gathered from three countries: United States, United Kingdom, and France. The SPL's depend on seven variables: frequency, polar direction angle, and five source state parameters: inner and outer nozzle pressure ratios, inner and outer stream total temperatures, and nozzle area ratio. A least-squares seven-dimensional curve fit defines a table of constants which is used for the prediction method. The resulting prediction has a mean error of 0 dB and a standard deviation of 1.2 dB. The prediction method is used to search for a coaxial jet which has the greatest coaxial noise benefit as compared with an equivalent single jet. It is found that benefits of about 6 dB are possible.

Zorumski, W. E.; Weir, D. S.

1982-01-01

149

Short-range shock formation and coalescence in numerical simulation of broadband noise propagation.  

PubMed

The number of jet and rocket noise studies has increased in recent years as researchers have sought to better understand aeroacoustic source and radiation characteristics. Although jet and rocket noise is finite-amplitude in nature, little is known about the existence of shock formation and coalescence close to the source. A numerical experiment is performed to propagate finite-amplitude noise and determine the extent of the nonlinearity over short distances with spherical spreading. The noise is filtered to have a haystack shape in the frequency domain, as is typical of such sources. The effect of the nonlinearity is compared in both the temporal and frequency domains as a function of distance. Additionally, the number of zero-crossings and overall sound pressure level is compared at several distances. The results indicate that the center frequency plays a particularly important role in the amount of coalescence and spectral redistribution that occurs. The general applicability of these results to actual near-field finite-amplitude jet and rocket noise experiments is also presented. PMID:20000901

Shepherd, Micah R; Gee, Kent L; Wochner, Mark S

2009-12-01

150

Subsonic and Supersonic Jet Noise Predictions from Statistical Source Models  

Microsoft Academic Search

Subsonicandsupersonicjetnoiseisdeterminednumerically from statisticalsourcemodels.Thegoalistodevelop prediction methods for high-speed jet noise for application to aeronautical and space transportation systems. In this framework, a combination of a k-? turbulence closure with an acoustic analogy provides an interesting way to compute such radiated acoustic é elds. Three acoustic analogies are investigated. First, the classical Lighthill theory in combination with Ribner' s results is applied

Christophe Bailly; Sébastien Candel; Philippe Lafon

1997-01-01

151

Heavy-Tailed Prediction Error: A Difficulty in Predicting Biomedical Signals of 1/f Noise Type  

PubMed Central

A fractal signal x(t) in biomedical engineering may be characterized by 1/f noise, that is, the power spectrum density (PSD) divergences at f = 0. According the Taqqu's law, 1/f noise has the properties of long-range dependence and heavy-tailed probability density function (PDF). The contribution of this paper is to exhibit that the prediction error of a biomedical signal of 1/f noise type is long-range dependent (LRD). Thus, it is heavy-tailed and of 1/f noise. Consequently, the variance of the prediction error is usually large or may not exist, making predicting biomedical signals of 1/f noise type difficult. PMID:23251226

Li, Ming; Zhao, Wei; Chen, Biao

2012-01-01

152

Broadband Low-Noise Monolithic GaAs Microwave Amplifiers with Very Low Power Consumption  

Microsoft Academic Search

A new general design phylosophy for producing cost-effective GaAs MMIC's is described. As a particular application, the design and the test results for wide-band and low-noise amplifier chips with an extremaly low power consumption are reported and discussed.

G. P. Donzelli; M. Pillan; L. Scopelliti; E. M. Bastida

1988-01-01

153

Noise characterization of broadband fiber Cherenkov radiation as a visible-wavelength  

E-print Network

on fiber supercontinuum generation are known to have high relative intensity noise and low spectral, "Supercontinuum generation in photonic crystal fiber," Rev. Mod. Phys. 78(4), 1135�1184 (2006). 5. Y. Wang, I. Keller, "Pulse compression with supercontinuum generation in microstructure fibers," J. Opt. Soc. Am. B

Boppart, Stephen

154

Prediction of flyover jet noise spectra from static tests  

NASA Technical Reports Server (NTRS)

A scaling law is derived for predicting the flyover noise spectra of a single-stream shock-free circular jet from static experiments. The theory is based on the Lighthill approach to jet noise. Density terms are retained to include the effects of jet heating. The influence of flight on the turbulent flow field is considered by an experimentally supported similarity assumption. The resulting scaling laws for the difference between one-third-octave spectra and the overall sound pressure level compare very well with flyover experiments with a jet engine and with wind tunnel experiments with a heated model jet.

Michel, U.; Michalke, A.

1981-01-01

155

Characterization and Analysis of Relative Intensity Noise in Broadband Optical Sources for Optical Coherence Tomography  

PubMed Central

Relative intensity noise (RIN) is one of the most significant factors limiting the sensitivity of an optical coherence tomography (OCT) system. The existing and prevalent theory being used for estimating RIN for various light sources in OCT is questionable, and cannot be applied uniformly for different types of sources. The origin of noise in various sources differs significantly, owing to the different physical nature of photon generation. In this study, we characterize and compare RIN of several OCT light sources including superluminescent diodes (SLDs), an erbium-doped fiber amplifier, multiplexed SLDs, and a continuous-wave laser. We also report a method for reduction of RIN by amplifying the SLD light output by using a gain-saturated semiconductor optical amplifier. PMID:22090794

Shin, Sunghwan; Sharma, Utkarsh; Tu, Haohua; Jung, Woonggyu; Boppart, Stephen A.

2011-01-01

156

Jet Engine Noise Generation, Prediction and Control. Chapter 86  

NASA Technical Reports Server (NTRS)

Aircraft noise has been a problem near airports for many years. It is a quality of life issue that impacts millions of people around the world. Solving this problem has been the principal goal of noise reduction research that began when commercial jet travel became a reality. While progress has been made in reducing both airframe and engine noise, historically, most of the aircraft noise reduction efforts have concentrated on the engines. This was most evident during the 1950 s and 1960 s when turbojet engines were in wide use. This type of engine produces high velocity hot exhaust jets during takeoff generating a great deal of noise. While there are fewer commercial aircraft flying today with turbojet engines, supersonic aircraft including high performance military aircraft use engines with similar exhaust flow characteristics. The Pratt & Whitney F100-PW-229, pictured in Figure la, is an example of an engine that powers the F-15 and F-16 fighter jets. The turbofan engine was developed for subsonic transports, which in addition to better fuel efficiency also helped mitigate engine noise by reducing the jet exhaust velocity. These engines were introduced in the late 1960 s and power most of the commercial fleet today. Over the years, the bypass ratio (that is the ratio of the mass flow through the fan bypass duct to the mass flow through the engine core) has increased to values approaching 9 for modern turbofans such as the General Electric s GE-90 engine (Figure lb). The benefits to noise reduction for high bypass ratio (HPBR) engines are derived from lowering the core jet velocity and temperature, and lowering the tip speed and pressure ratio of the fan, both of which are the consequences of the increase in bypass ratio. The HBPR engines are typically very large in diameter and can produce over 100,000 pounds of thrust for the largest engines. A third type of engine flying today is the turbo-shaft which is mainly used to power turboprop aircraft and helicopters. An example of this type of engine is shown in Figure IC, which is a schematic of the Honeywell T55 engine that powers the CH-47 Chinook helicopter. Since the noise from the propellers or helicopter rotors is usually dominant for turbo-shaft engines, less attention has been paid to these engines in so far as community noise considerations are concerned. This chapter will concentrate mostly on turbofan engine noise and will highlight common methods for their noise prediction and reduction.

Huff, Dennis L.; Envia, Edmane

2004-01-01

157

Structural Acoustic Prediction and Interior Noise Control Technology  

NASA Technical Reports Server (NTRS)

This report documents the results of Task 14, "Structural Acoustic Prediction and Interior Noise Control Technology". The task was to evaluate the performance of tuned foam elements (termed Smart Foam) both analytically and experimentally. Results taken from a three-dimensional finite element model of an active, tuned foam element are presented. Measurements of sound absorption and sound transmission loss were taken using the model. These results agree well with published data. Experimental performance data were taken in Boeing's Interior Noise Test Facility where 12 smart foam elements were applied to a 757 sidewall. Several configurations were tested. Noise reductions of 5-10 dB were achieved over the 200-800 Hz bandwidth of the controller. Accelerometers mounted on the panel provided a good reference for the controller. Configurations with far-field error microphones outperformed near-field cases.

Mathur, G. P.; Chin, C. L.; Simpson, M. A.; Lee, J. T.; Palumbo, Daniel L. (Technical Monitor)

2001-01-01

158

Jet noise prediction using the Lighthill acoustic analogy  

NASA Astrophysics Data System (ADS)

A jet noise source model based on the Lighthill acoustic analogy is presented. Although much of the theory used is well known, a new feature of the model is the inclusion of frequency dependence for the time and length scales used in the turbulence two-point correlation function. It is found that allowing for this experimentally observed dependence markedly improves the agreement of the model's prediction with experimental far-field data. To illustrate this agreement the case of a single turbulent jet is considered. Using well-respected scaling laws for the mean and turbulent properties of such jets a prediction for a single jet noise spectrum is obtained which shows very good agreement with the prediction using the empirically based ESDU database. The effect of altering the frequency dependence of the moving axis timescale is briefly discussed and it is indicated how the source model can be generalized to use RANS and other CFD data to predict jet noise, for single and coaxial jets and also for more novel nozzle geometries.

Self, R. H.

2004-08-01

159

The MDE method for aircraft cabin interior noise prediction  

NASA Astrophysics Data System (ADS)

This paper describes a finite-element method, based on the matrix difference equation (MDE) method of Denke (1979), for predicting aircraft-cabin interior noise, using coupled structural-acoustic models to represent the fuselage structure and the air inside. In this method, the problem of modeling coupled structural-acoustic systems is solved by the FEM, employing displacements as the unknown variables. The method is shown to be efficient enough to be employed as a design tool.

Denke, P. H.

1989-09-01

160

Predicting Rocket or Jet Noise in Real Time  

NASA Technical Reports Server (NTRS)

A semi-empirical theoretical model and a C++ computer program that implements the model have been developed for use in predicting the noise generated by a rocket or jet engine. The computer program, entitled the Realtime Rocket and Jet Engine Noise Analysis and Prediction Software, is one of two main subsystems of the Acoustic Prediction/Measurement Tool, which comprises software, acoustic instrumentation, and electronic hardware combined to afford integrated capabilities for real-time prediction and measurement of noise emitted by rocket and jet engines. [The other main subsystem, consisting largely of acoustic instrumentation and electronic hardware, is described in Wireless Acoustic Measurement System, which appears elsewhere in this section.] The theoretical model was derived from the fundamental laws of fluid mechanics, as first was done by M. J. Lighthill in his now famous theory of aerodynamically generated sound. The far-field approximation of the Lighthill theory is incorporated into this model. Many other contributions from various researchers have also been introduced into the model. The model accounts for two noise components: shear noise and self noise. The final result of the model is expressed in terms of a volume integral of the acoustic intensities attributable to these two components, subject to various directivity coefficients. The computer program was written to solve the volume integral. The inputs required by the program are two data files from a computational fluid dynamics (CFD) simulation of the flow of interest: the computational-grid file and the solution file. The CFD solution should be one that has been obtained for conditions that closely approximate those of an experimental test that is yet to be performed. In the current state of development of the model and software, it is recommended that the observation points lie along a radius at an angle >60 from the jet axis. The software provides, and is driven via, a graphical user interface, which facilitates its use. Optionally, the program accepts additional input in the form of data on the measured sound pressure level as a function of frequency at a given far-field location, preferably at an angle of 90 from the jet axis. The user is prompted to use default empirical constants or to choose constants based the measurement data. The user can view the results and compare them with other computational or experimental data. Once satisfied with the results, the user can save a graph of the results in a file that can be imported into documents.

Frendi, Kader

2007-01-01

161

Assessment of noise impact on the urban environment: a study on noise-prediction models. Environmental health series  

SciTech Connect

The report identifies, compares, and evaluates the major methods developed in Europe and North America to predict noise levels resulting from urban-development projects. Hopefully, it will guide countries that have not yet developed their own noise-prediction models to choose the model most appropriate for their particular situation. It covers prediction methods for road traffic noise and railroad traffic noise in Austria, Czecheslovakia, France, both Germany's Hungary, Netherlands, Scandinavia, Switzerland, U.K. and USA, as well as the Commission of the European Communities, and a comparison of methods. It also covers prediction methods for industrial noise from Austria, both Germany's Netherlands, Scandinavia, and U.K., and discusses calculation methods for aircraft noise around airports.

Lang, J.

1986-01-01

162

Noise prediction of a subsonic turbulent round jet using the lattice-Boltzmann method.  

PubMed

The lattice-Boltzmann method (LBM) was used to study the far-field noise generated from a Mach, M(j)=0.4, unheated turbulent axisymmetric jet. A commercial code based on the LBM kernel was used to simulate the turbulent flow exhausting from a pipe which is 10 jet radii in length. Near-field flow results such as jet centerline velocity decay rates and turbulence intensities were in agreement with experimental results and results from comparable LES studies. The predicted far field sound pressure levels were within 2 dB from published experimental results. Weak unphysical tones were present at high frequency in the computed radiated sound pressure spectra. These tones are believed to be due to spurious sound wave reflections at boundaries between regions of varying voxel resolution. These "VR tones" did not appear to bias the underlying broadband noise spectrum, and they did not affect the overall levels significantly. The LBM appears to be a viable approach, comparable in accuracy to large eddy simulations, for the problem considered. The main advantages of this approach over Navier-Stokes based finite difference schemes may be a reduced computational cost, ease of including the nozzle in the computational domain, and ease of investigating nozzles with complex shapes. PMID:20815448

Lew, Phoi-Tack; Mongeau, Luc; Lyrintzis, Anastasios

2010-09-01

163

Noise prediction of a subsonic turbulent round jet using the lattice-Boltzmann method  

PubMed Central

The lattice-Boltzmann method (LBM) was used to study the far-field noise generated from a Mach, Mj=0.4, unheated turbulent axisymmetric jet. A commercial code based on the LBM kernel was used to simulate the turbulent flow exhausting from a pipe which is 10 jet radii in length. Near-field flow results such as jet centerline velocity decay rates and turbulence intensities were in agreement with experimental results and results from comparable LES studies. The predicted far field sound pressure levels were within 2 dB from published experimental results. Weak unphysical tones were present at high frequency in the computed radiated sound pressure spectra. These tones are believed to be due to spurious sound wave reflections at boundaries between regions of varying voxel resolution. These “VR tones” did not appear to bias the underlying broadband noise spectrum, and they did not affect the overall levels significantly. The LBM appears to be a viable approach, comparable in accuracy to large eddy simulations, for the problem considered. The main advantages of this approach over Navier–Stokes based finite difference schemes may be a reduced computational cost, ease of including the nozzle in the computational domain, and ease of investigating nozzles with complex shapes. PMID:20815448

Lew, Phoi-Tack; Mongeau, Luc; Lyrintzis, Anastasios

2010-01-01

164

Prediction of Turbulent Jet Mixing Noise Reduction by Water Injection  

NASA Technical Reports Server (NTRS)

A one-dimensional control volume formulation is developed for the determination of jet mixing noise reduction due to water injection. The analysis starts from the conservation of mass, momentum and energy for the confrol volume, and introduces the concept of effective jet parameters (jet temperature, jet velocity and jet Mach number). It is shown that the water to jet mass flow rate ratio is an important parameter characterizing the jet noise reduction on account of gas-to-droplet momentum and heat transfer. Two independent dimensionless invariant groups are postulated, and provide the necessary relations for the droplet size and droplet Reynolds number. Results are presented illustrating the effect of mass flow rate ratio on the jet mixing noise reduction for a range of jet Mach number and jet Reynolds number. Predictions from the model show satisfactory comparison with available test data on perfectly expanded hot supersonic jets. The results suggest that significant noise reductions can be achieved at increased flow rate ratios.

Kandula, Max

2008-01-01

165

Prediction, Measurement, and Suppression of High Temperature Supersonic Jet Noise  

NASA Technical Reports Server (NTRS)

The photograph in figure 1 displays a water cooled round convergent-divergent supersonic nozzle operating slightly overexpanded near 2460 F. The nozzle is designed to produce shock free flow near this temperature at Mach 2. The exit diameter of this nozzle is 3.5 inches. This nozzle is used in the present study to establish properties of the sound field associated with high temperature supersonic jets operating fully pressure balanced (i.e. shock free) and to evaluate capability of the compressible Rayleigh model to account for principle physical features of the observed sound emission. The experiment is conducted statically (i.e. M(sub f) = 0.) in the NASA/LaRC Jet Noise Laboratory. Both aerodynamic and acoustic measurements are obtained in this study along with numerical plume simulation and theoretical prediction of jet noise. Detailed results from this study are reported previously by Seiner, Ponton, Jansen, and Lagen.

Seiner, John M.; Bhat, T. R. S.; Jansen, Bernard J.

1999-01-01

166

'Integral Noise': An automatic calculation model for the prediction and control of fixed-wing aircraft noise. I - General considerations, theoretical bases and model analysis  

Microsoft Academic Search

A description is given of the INTNOI Integral Noise Program for advanced aircraft noise prediction and control. This computer model performs, on a modular basis, the analysis of both boundary layer aerodynamic noise and engine noise for the case of such turbofan-powered commercial aircraft as the 737. It also permits the prediction of noise levels due to engine and aerodynamic

F. Bossa; R. Gualdi

1981-01-01

167

Near-field noise prediction for aircraft in cruising flight: Methods manual. [laminar flow control noise effects analysis  

NASA Technical Reports Server (NTRS)

Methods for predicting noise at any point on an aircraft while the aircraft is in a cruise flight regime are presented. Developed for use in laminar flow control (LFC) noise effects analyses, they can be used in any case where aircraft generated noise needs to be evaluated at a location on an aircraft while under high altitude, high speed conditions. For each noise source applicable to the LFC problem, a noise computational procedure is given in algorithm format, suitable for computerization. Three categories of noise sources are covered: (1) propulsion system, (2) airframe, and (3) LFC suction system. In addition, procedures are given for noise modifications due to source soundproofing and the shielding effects of the aircraft structure wherever needed. Sample cases, for each of the individual noise source procedures, are provided to familiarize the user with typical input and computed data.

Tibbetts, J. G.

1979-01-01

168

The Role of Instability Waves in Predicting Jet Noise  

NASA Technical Reports Server (NTRS)

Debate over whether linear instability waves play a role in the prediction of jet noise has been going on for many years. Parallel mean flow models, such as the one proposed by Lilley, usually neglect these waves because they cause the solution to become infinite. The present paper solves the true non-parallel acoustic equations for a two-dimensional shear layer by using a vector Greens function and assuming small mean flow spread rate. The results show that linear instability waves must be accounted for in order to construct a proper causal solution to the problem.

Goldstein, Marvin E.; Handler, Louis M.

2003-01-01

169

Auralization of Hybrid Wing Body Aircraft Flyover Noise from System Noise Predictions  

NASA Technical Reports Server (NTRS)

System noise assessments of a state-of-the-art reference aircraft (similar to a Boeing 777-200ER with GE90-like turbofan engines) and several hybrid wing body (HWB) aircraft configurations were recently performed using NASA engine and aircraft system analysis tools. The HWB aircraft were sized to an equivalent mission as the reference aircraft and assessments were performed using measurements of airframe shielding from a series of propulsion airframe aeroacoustic experiments. The focus of this work is to auralize flyover noise from the reference aircraft and the best HWB configuration using source noise predictions and shielding data based largely on the earlier assessments. For each aircraft, three flyover conditions are auralized. These correspond to approach, sideline, and cutback operating states, but flown in straight and level flight trajectories. The auralizations are performed using synthesis and simulation tools developed at NASA. Audio and visual presentations are provided to allow the reader to experience the flyover from the perspective of a listener in the simulated environment.

Rizzi, Stephen A.; Aumann, Aric R.; Lopes, Leonvard V.; Burley, Casey L.

2013-01-01

170

Prediction of flyover jet noise spectra from static tests  

NASA Astrophysics Data System (ADS)

A scaling law for predicting the overall flyover noise of a single stream shock-free circular jet from static experiments is outlined. It is valid for isothermal and hot jets. It assumes that the jet flow and turbulence field are axially stretched in flight. Effects of the boundary layer within the nozzle and along the engine nacelle are neglected. The scaling laws for the power spectral density and spectra with constant relative bandwidth can be derived. In order to compare static and inflight directivities, the far field point relative to the source position must be denoted by the emission angle and the wave normal distance. From the solution of the convective Lighthill equation in a coordinate system fixed to the jet nozzle (wind tunnel case), the power spectral density of sound pressure at a given frequency is found. Predictions for Aerotrain compare well with measured values.

Michel, U.; Michalke, A.

171

Progress Toward Improving Jet Noise Predictions in Hot Jets  

NASA Technical Reports Server (NTRS)

An acoustic analogy methodology for improving noise predictions in hot round jets is presented. Past approaches have often neglected the impact of temperature fluctuations on the predicted sound spectral density, which could be significant for heated jets, and this has yielded noticeable acoustic under-predictions in such cases. The governing acoustic equations adopted here are a set of linearized, inhomogeneous Euler equations. These equations are combined into a single third order linear wave operator when the base flow is considered as a locally parallel mean flow. The remaining second-order fluctuations are regarded as the equivalent sources of sound and are modeled. It is shown that the hot jet effect may be introduced primarily through a fluctuating velocity/enthalpy term. Modeling this additional source requires specialized inputs from a RANS-based flowfield simulation. The information is supplied using an extension to a baseline two equation turbulence model that predicts total enthalpy variance in addition to the standard parameters. Preliminary application of this model to a series of unheated and heated subsonic jets shows significant improvement in the acoustic predictions at the 90 degree observer angle.

Khavaran, Abbas; Kenzakowski, Donald C.

2007-01-01

172

Broadband Liner Optimization for the Source Diagnostic Test Fan  

NASA Technical Reports Server (NTRS)

The broadband component of fan noise has grown in relevance with the utilization of increased bypass ratio and advanced fan designs. Thus, while the attenuation of fan tones remains paramount, the ability to simultaneously reduce broadband fan noise levels has become more appealing. This paper describes a broadband acoustic liner optimization study for the scale model Source Diagnostic Test fan. Specifically, in-duct attenuation predictions with a statistical fan source model are used to obtain optimum impedance spectra over a number of flow conditions for three liner locations in the bypass duct. The predicted optimum impedance information is then used with acoustic liner modeling tools to design liners aimed at producing impedance spectra that most closely match the predicted optimum values. Design selection is based on an acceptance criterion that provides the ability to apply increased weighting to specific frequencies and/or operating conditions. Typical tonal liner designs targeting single frequencies at one operating condition are first produced to provide baseline performance information. These are followed by multiple broadband design approaches culminating in a broadband liner targeting the full range of frequencies and operating conditions. The broadband liner is found to satisfy the optimum impedance objectives much better than the tonal liner designs. In addition, the broadband liner is found to provide better attenuation than the tonal designs over the full range of frequencies and operating conditions considered. Thus, the current study successfully establishes a process for the initial design and evaluation of novel broadband liner concepts for complex engine configurations.

Nark, Douglas M.; Jones, Michael G.

2012-01-01

173

Computation of rotor wake turbulence noise  

NASA Astrophysics Data System (ADS)

A major source of fan broadband noise is the interaction of rotor wake turbulence with the fan outlet guide vanes. A broadband noise model that utilizes computed rotor flow turbulence from a Reynolds averaged Navier-Stokes code is used to predict fan broadband noise spectra. The noise model is employed to examine the broadband noise characteristics of the 22-in source diagnostic test fan rig for which broadband noise data were obtained in wind tunnel tests at the NASA Glenn Research Center. A 9-case matrix of three outlet guide vane configurations at three representative fan tip speeds are considered. For all cases inlet and exhaust spectra of acoustic power are computed and compared with the measured spectra where possible. The acoustic power levels and shape of the predicted spectra are in good agreement with the measured data for the fan exhaust duct radiation at approach condition where direct comparisons are possible. The predicted spectra show the experimentally observed trends with fan tip speed, vane count and vane sweep. The results also demonstrate the validity of using computational fluid dynamics based turbulence information for fan broadband noise calculations.

Nallasamy, M.; Envia, E.

2005-04-01

174

Hearing threshold and heart rate in men after repeated exposure to dynamic muscle work, sinusoidal vs stochastic whole body vibration and stable broadband noise.  

PubMed

Changes in the temporary hearing threshold ( TTS2 ) and heart rate (HR) were examined in subjects exposed to stable noise, whole body vibration and dynamic muscular work at a dry-bulb temperature of 30 degrees C. The exposure combinations consisted of three categories of dynamic muscular work with varying loads ( 2W , 4W , 8W ), of two categories of noise and of three categories of vibration. The noise categories were: (1) no noise, and (2) stable, broadband (bandwidth 0.2-16.0 kHz) A-weighted noise with an intensity of 90 dB. The vibration categories were: (1) no vibration, (2) sinusoidal whole body vibration (Z-axis) with a frequency of 5 Hz, and (3) stochastic broadband (bandwidth 2.8-11.2 Hz) whole body vibration. A single test consisted of a control period of 30 min, three consecutive exposure periods of 16 min, each followed by a 4-min post-exposure interval and a recovery period of 15 min. The results of the variance analyses indicated that noise had the most notable effect on the TTS2 values at the hearing frequencies of both 4 and 6 kHz. Of the paired combinations, noise plus vibration and noise plus dynamic muscular work caused the most obvious combined effects. The combined effect of all three factors (noise, vibration and work) on the TTS2 values after three consecutive exposure periods was significant at the 2.5% level at the 4 kHz hearing frequency and at the 5% level at the 6 kHz hearing frequency. The added effect of vibration on enhanced TTS2 values was particularly clear when the vibration was stochastic and when the subjects had a low ( 2W ) working efficiency. Increasing the working efficiency, on the other hand, seemed to retard increases in the hearing threshold. Thus TTS2 values seemed to reflect the changes in HR values. It is as if the low rate of cardiovascular activity during light dynamic muscular work had enabled the manifestation of the cardiovascular effects of noise and vibration; during strenuous dynamic muscular work, however, the high rate of cardiovascular activity aimed in some way at compensating for the effects of noise and vibration on blood circulation. PMID:6724700

Manninen, O

1984-01-01

175

Three-dimensional effects on pure tone fan noise due to inflow distortion. [rotor blade noise prediction  

NASA Technical Reports Server (NTRS)

Two dimensional, quasi three dimensional and three dimensional theories for the prediction of pure tone fan noise due to the interaction of inflow distortion with a subsonic annular blade row were studied with the aid of an unsteady three dimensional lifting surface theory. The effects of compact and noncompact source distributions on pure tone fan noise in an annular cascade were investigated. Numerical results show that the strip theory and quasi three-dimensional theory are reasonably adequate for fan noise prediction. The quasi three-dimensional method is more accurate for acoustic power and model structure prediction with an acoustic power estimation error of about plus or minus 2db.

Kobayashi, H.

1978-01-01

176

Effect of Large-Eddy Simulation Fidelity on Predicted Mechanisms of Jet Noise Reduction  

E-print Network

Effect of Large-Eddy Simulation Fidelity on Predicted Mechanisms of Jet Noise Reduction Jeonglae an unexpectedly subtle importance of accurate numerics for predicting and reducing turbulent jet noise. We observe jet axis I. Introduction JET NOISE is an important factor in aircraft certification worldwide. Early

Freund, Jonathan B.

177

Broadband ocean bottom seismometer in the Gulf of Cadiz (offshore SW Iberia and NW of Moroccan margin): Characterization of ambient noise and tomographic model of the crustal structure.  

NASA Astrophysics Data System (ADS)

In this study we use the continuous data recording performed by 24 ocean bottom seismometers (OBS), wide band (BB), deployed in the Gulf of Cadiz in the framework of the NEAREST project from September 2007 to July of 2008 to study the ambient seismic noise recorded in the bottom of the ocean. Our goals are: i) to understand the instrument and the environmental conditions that control the observed seismic noise; ii) and to obtain reliable broadband surface wave dispersion measurements. The noise sources are investigated through the probability density functions (PDFs) of power spectral density (PSDs) which provides insights on the generation and propagating of seismic noise in the Gulf of Cadiz. We show the results of the Rayleigh wave group velocity tomography performed using ambient seismic noise observed on 24 broadband OBS in the Gulf of Cadiz and 7 broadband land stations south of Portugal. The time-series for the 11 months were cross-correlated to obtain empirical Rayleigh wave green's functions between the components OBS vertical-OBS vertical, OBS vertical-land station vertical, OBS hydrophone-OBS hydrophone and between OBS hydrophone-Land station vertical. The results are based on the analysis of two spectral bands corresponding to the primary (10-20s) and secondary (5-10s) microseism peak. The stack of the station-to-station cross correlograms was done to increase the signal-to-noise ratio. In addition to the usual stack, we have also have applied a phase-weighted stack to avoid local noise contamination and so enable the detection of weak coherent signals. These cross-correlograms enabled us to compute short-period surface-wave group-velocity measurements on interstation paths. We used these measurements to construct maps of Rayleigh-wave group-velocity lateral variations at different periods at the Gulf of Cadiz and south of Portugal. Despite the great difference in the crustal structure below the OBS (thin continental or oceanic type) and the land stations (typical continental crust, 30 km thick) we were able to derive high S/N cross-correlations between these two types of sensors. This study was co-sponsored by several projects namely the NEAREST FP6-2005-GLOBAL-4 (OJ 2005 C177/15), WILAS (PTDC/CTE-GIX/097946/2008), TOPOMED (TOPOEUROPE/0001/2007) and Pest OE/CTE/LA0019/2011.

Corela, Carlos; Silveira, Graça; Matias, Luis; Schimmel, Martin; Geissler, Wolfram

2013-04-01

178

Numerical method for predicting ship propeller cavitation noise  

Microsoft Academic Search

During ship travels in high-velocity, propeller cavitation noise predominates in the radiated noise sources. However, experiential data regress method was use to predicate propeller cavitation noise in the past. In this article, propeller cavitation noise has been calculated by numerical computation method. From the engineering point of view, ship propeller has been disposed as a dipole bubble. Bubble volume pulse

Yong-Kun Zhang; Ying Xiong

2011-01-01

179

Broadband sub-millimeter wave amplifer module with 38dB gain and 8.3dB noise figure  

NASA Astrophysics Data System (ADS)

Broadband sub-millimeter wave technology has received significant attention for potential applications in security, medical, and military imaging. Despite theoretical advantages of reduced size, weight, and power compared to current millimeter-wave systems, sub-millimeter-wave systems are hampered by a fundamental lack of amplification with sufficient gain and noise figure properties. We report on the development of a sub-millimeter wave amplifier module as part of a broadband pixel operating from 300-350 GHz, biased off of a single 2V power supply. Over this frequency range, > 38 dB gain and < 8.3 dB noise figure are obtained and represent the current state-of-art performance capabilities. The prototype pixel chain consists of two WR3 waveguide amplifier blocks, and a horn antenna and diode detector. The low noise amplifier Sub-Millimeter-wave Monolithic Integrated Circuit (SMMIC) was originally developed under the DARPA SWIFT and THz Electronics programs and is based on sub 50 nm Indium Arsenide Composite Channel (IACC) transistor technology with a projected maximum oscillation frequency fmax > 1.0 THz. This development and demonstration may bring to life future sub-millimeter-wave and THz applications such as solutions to brown-out problems, ultra-high bandwidth satellite communication cross-links, and future planetary exploration missions.

Sarkozy, S.; Leong, K.; Lai, R.; Leakey, R.; Yoshida, W.; Mei, X.; Lee, J.; Liu, P.-H.; Gorospe, B.; Deal, W. R.

2011-05-01

180

Prediction of acoustic scattering in the time domain and its applications to rotorcraft noise  

NASA Astrophysics Data System (ADS)

This work aims at the development of a numerical method for the analysis of acoustic scattering in the time domain and its applications to rotorcraft noise. This purpose is achieved by developing two independent methods: (1) an analytical formulation of the pressure gradient for an arbitrary moving source and (2) a time-domain moving equivalent source method. First, the analytical formulation for the pressure gradient is developed to fulfill the boundary condition on a scattering surface to account for arbitrary moving incident sources. A semi-analytical formulation was derived from the gradient of the Ffowcs Williams-Hawkings (FW-H) equation. This formulation needs to calculate the observer time differentiation outside the integrals numerically. A numerical algorithm is developed to implement this formulation in an aeroacoustic prediction code. A new analytical formulation is presented in the thesis. In this formulation, the time differentiation is taken inside the integrals analytically. This formulation avoids the numerical time differentiation with respect to the observer time, which is computationally more efficient. The acoustic pressure gradient predicted by these two formulations is validated through comparison with available exact solutions for a stationary and moving monopole sources. The agreement between the predictions and exact solutions is excellent. One of the advantages of this analytic formulation is that it efficiently provides the boundary condition for the acoustic scattering of sound generated from an arbitrary moving source, such as rotating blades, which undergoes rotation, flapping and lead-lag motions. The formulation is applied to the rotor noise problems for two model rotors (UH-1H and HART-I). For HART-I rotor, CFD/CSD coupling was used to provide unsteady aerodynamics and trim solutions of the blade motion. A purely numerical approach is compared with the analytical formulations. The agreement between the analytical formulations and the numerical method is excellent for both stationary and moving observer cases. The formulation for the pressure gradient is first used to predict acoustic scattering in the frequency domain. The prediction is validated with the exact solution for acoustic scattering generated by a monopole source by a stationary sphere. A Bo105 helicopter and a notional heavy lift quad tilt rotor are considered to demonstrate a potential significance of acoustic scattering of rotorcraft noise. NASA's Fast Scattering Code is used for the frequency-domain scattering solver. Secondly, a new and efficient time domain acoustic scattering method using a moving equivalent source is developed to predict acoustic scattering in the time domain efficiently. The time-domain method provides entire frequency solutions in a single computation and is able to predict acoustic scattering of aperiodic signals. The method assumes an acoustically rigid surface for a scattering body and neglects the refraction effect by non-uniform flow around the scattering body. The pressure-gradient boundary condition is determined on a scattering surface and then the scattered field is calculated by using equivalent sources located within the scattering surface. Linear shape functions are used to discretize the strength of the equivalent sources in time and singular value decomposition is used to overcome potential numerical instability. The detailed numerical algorithm is addressed in the thesis. The method is more efficient numerically and easier to implement than other time-domain methods using a finite difference scheme or boundary integral equations because it is not necessary to find the solution in the entire domain, it uses a fewer number of equivalent sources than the surface mesh points, and it does not involve surface integrals. The method is validated against exact solutions for various cases including a single frequency monopole source, a dipole source, multiple sources, beat, and broadband noise sources. The predictions are found to be in excellent agreement with the exact solutions. The effect of

Lee, Seongkyu

181

Broadband teleportation  

E-print Network

Quantum teleportation of an unknown broadband electromagnetic field is investigated. The continuous-variable teleportation protocol by Braunstein and Kimble [Phys. Rev. Lett. {\\bf 80}, 869 (1998)] for teleporting the quantum state of a single mode of the electromagnetic field is generalized for the case of a multimode field with finite bandwith. We discuss criteria for continuous-variable teleportation with various sets of input states and apply them to the teleportation of broadband fields. We first consider as a set of input fields (from which an independent state preparer draws the inputs to be teleported) arbitrary pure Gaussian states with unknown coherent amplitude (squeezed or coherent states). This set of input states, further restricted to an alphabet of coherent states, was used in the experiment by Furusawa {\\it et al.} [Science {\\bf 282}, 706 (1998)]. It requires unit-gain teleportation for optimizing the teleportation fidelity. In our broadband scheme, the excess noise added through unit-gain teleportation due to the finite degree of the squeezed-state entanglement is just twice the (entanglement) source's squeezing spectrum for its ``quiet quadrature.'' The teleportation of one half of an entangled state (two-mode squeezed vacuum state), i.e., ``entanglement swapping,'' and its verification are optimized under a certain nonunit gain condition. We will also give a broadband description of this continuous-variable entanglement swapping based on the single-mode scheme by van Loock and Braunstein [Phys. Rev. A {\\bf 61}, 10302 (2000)

P. van Loock; Samuel L. Braunstein; H. J. Kimble

1999-02-08

182

Investigation of the Jet Noise Prediction Theory and Application Utilizing the PAO Formulation. [mathematical model for calculating noise radiation  

NASA Technical Reports Server (NTRS)

Application of the Phillips theory to engineering calculations of rocket and high speed jet noise radiation is reported. Presented are a detailed derivation of the theory, the composition of the numerical scheme, and discussions of the practical problems arising in the application of the present noise prediction method. The present method still contains some empirical elements, yet it provides a unified approach in the prediction of sound power, spectrum, and directivity.

1973-01-01

183

The Role of Instability Waves in Predicting Jet Noise  

NASA Technical Reports Server (NTRS)

There has been an ongoing debate about the role of linear instability waves in the prediction of jet noise. Parallel mean flow models, such as the one proposed by Lilley, usually neglect these waves because they cause the solution to become infinite. The resulting solution is then non-causal and can, therefore, be quite different from the true causal solution for the chaotic flows being considered here. The present paper solves the relevant acoustic equations for a non-parallel mean flow by using a vector Green s function approach and assuming the mean flow to be weakly non-parallel, i.e., assuming the spread rate to be small. It demonstrates that linear instability waves must be accounted for in order to construct a proper causal solution to the jet noise problem. . Recent experimental results (e.g., see Tam, Golebiowski, and Seiner,1996) show that the small angle spectra radiated by supersonic jets are quite different from those radiated at larger angles (say, at 90deg) and even exhibit dissimilar frequency scalings (i.e., they scale with Helmholtz number as opposed to Strouhal number). The present solution is (among other things )able to explain this rather puzzling experimental result.

Goldstein, M. E.; Leib, S. J.

2004-01-01

184

A Study on Predicting Shinkansen Noise Levels Using the Sound Intensity Method  

NASA Astrophysics Data System (ADS)

The purpose of this paper is to demonstrate a new method developed to predict track wayside noise levels resulting from the passage of high-speed trains. The method calculates noise levels based on data acquired by the sound intensity method developed by the Central Japan Railway Company. This measurement method allows one to identify each sound source and its characteristics as well as identify how much each source contributes to the overall resulting noise level. Structure borne noise and multiple reflected noise between train car bodies and noise barriers are also studied. As a result of this study, a prediction method was created which can calculate and predict noise levels resulting from such various factors as structure, train type, train speed and noise barrier. Noise levels predicted during this study agreed well with those actually measured under various conditions, thus indicating the prediction method model resulting from the study is a useful tool to verify noise levels occurring at receiver positions. Furthermore, it can also verify in advance how much effect noise barriers or train source noise level reduction devices would have on noise reduction.

Okada, Tadashi

185

Transmission of gear noise to aircraft interiors prediction methods  

NASA Astrophysics Data System (ADS)

Prediction of interior noise of helicopters due to drive train vibration ideally requires an analytical model of the entire dynamic system including airframe, transmission, and all attachments. The development of such a model is beset with numerous difficulties. The need for such model is addressed, as is certain of the critical issues involved: the inadequacy of finite element modeling in the acoustic frequency range; the costs associated with assessment of parametric variations; the difficulty of incorporating new technology into existing computer programs. Potential solutions to these problems are discussed: use of combined test and analysis (system identification) to obtain better models; component synthesis using frequency domain reduced models; a computer program known as DYSCO. This program has a general capability to modify and couple components in the time or frequency domain and can act as a repository for the latest analytical developments.

Berman, A.

1985-01-01

186

Fan Noise Source Diagnostic Test Computation of Rotor Wake Turbulence Noise  

NASA Astrophysics Data System (ADS)

An important source mechanism of fan broadband noise is the interaction of rotor wake turbulence with the fan outlet guide vanes. A broadband noise model that utilizes computed rotor flow turbulence from a RANS code is used to predict fan broadband noise spectra. The noise model is employed to examine the broadband noise characteristics of the 22-inch Source Diagnostic Test fan rig for which broadband noise data were obtained in wind tunnel tests at the NASA Glenn Research Center. A 9-case matrix of three outlet guide vane configurations at three representative fan tip speeds are considered. For all cases inlet and exhaust acoustic power spectra are computed and compared with the measured spectra where possible. In general, the acoustic power levels and shape of the predicted spectra are in good agreement with the measured data. The predicted spectra show the experimentally observed trends with fan tip speed, vane count, and vane sweep. The results also demonstrate the validity of using CFD-based turbulence information for fan broadband noise calculations.

Nallasamy, M.; Envia, E.; Thorp, S. A.; Shabbir, A.

2002-08-01

187

Fan Noise Source Diagnostic Test Computation of Rotor Wake Turbulence Noise  

NASA Technical Reports Server (NTRS)

An important source mechanism of fan broadband noise is the interaction of rotor wake turbulence with the fan outlet guide vanes. A broadband noise model that utilizes computed rotor flow turbulence from a RANS code is used to predict fan broadband noise spectra. The noise model is employed to examine the broadband noise characteristics of the 22-inch Source Diagnostic Test fan rig for which broadband noise data were obtained in wind tunnel tests at the NASA Glenn Research Center. A 9-case matrix of three outlet guide vane configurations at three representative fan tip speeds are considered. For all cases inlet and exhaust acoustic power spectra are computed and compared with the measured spectra where possible. In general, the acoustic power levels and shape of the predicted spectra are in good agreement with the measured data. The predicted spectra show the experimentally observed trends with fan tip speed, vane count, and vane sweep. The results also demonstrate the validity of using CFD-based turbulence information for fan broadband noise calculations.

Nallasamy, M.; Envia, E.; Thorp, S. A.; Shabbir, A.

2002-01-01

188

A study of the prediction of cruise noise and laminar flow control noise criteria for subsonic air transports  

NASA Technical Reports Server (NTRS)

General procedures for the prediction of component noise levels incident upon airframe surfaces during cruise are developed. Contributing noise sources are those associated with the propulsion system, the airframe and the laminar flow control (LFC) system. Transformation procedures from the best prediction base of each noise source to the transonic cruise condition are established. Two approaches to LFC/acoustic criteria are developed. The first is a semi-empirical extension of the X-21 LFC/acoustic criteria to include sensitivity to the spectrum and directionality of the sound field. In the second, the more fundamental problem of how sound excites boundary layer disturbances is analyzed by deriving and solving an inhomogeneous Orr-Sommerfeld equation in which the source terms are proportional to the production and dissipation of sound induced fluctuating vorticity. Numerical solutions are obtained and compared with corresponding measurements. Recommendations are made to improve and validate both the cruise noise prediction methods and the LFC/acoustic criteria.

Swift, G.; Mungur, P.

1979-01-01

189

[The computer simulating prediction method of noise of underground garage in urban residential region].  

PubMed

The model of random point sound source was applied to predict the noise of underground garage in urban residential region with the method of computer simulating. Comparing the predict data and the data of measurement, the precision of this model was good. The model can be applied to predict the influence of the noise of new built underground garage noise, it can offer the reference for the planning department. PMID:14551978

Zhang, Bangjun; Shi, Lili; Di, Guoqin

2003-07-01

190

Estimation and prediction of noise power based on variational Bayesian and adaptive ARMA time series  

NASA Astrophysics Data System (ADS)

Estimation and prediction of noise power are very important for communication anti-jamming and efficient allocation of spectrum resources in adaptive wireless communication and cognitive radio. In order to estimate and predict the time-varying noise power caused by natural factors and jamming in the high frequency channel, Variational Bayesian algorithm and adaptive ARMA time series are proposed. Through establishing the time-varying noise power model, which controlled by the noise variance rate, the noise power can be estimated with Variational Bayesian algorithm, and the results show that the estimation error is related to observation interval. What's more, through the analysis of the correlation characteristics of the estimation power, noise power can be predicted based on adaptive ARMA time series, and the results show that it will be available to predict the noise power in next 5 intervals with the proportional error less than 0.2.

Zhang, Jingyi; Li, Yonggui; Zhu, Yonggang; Li, Binwu

2014-04-01

191

Prediction of wind noise radiated from passenger cars and its evaluation based on auralization  

Microsoft Academic Search

This paper describes the prediction of radiated wind noise from automobiles and its reduction. The Lighthill acoustic analogy was employed to estimate the wind noise at far field. In order to compute accurate pressure fluctuations, which play a role as the noise sources in the analogy, an overlapped grid system is used to calculate flow fields in detail with a

Kenji Ono; Ryutaro Himeno; Tatsuya Fukushima

1999-01-01

192

Simulation of a hot coaxial jet: Direct noise prediction and flow-acoustics correlations  

E-print Network

Simulation of a hot coaxial jet: Direct noise prediction and flow-acoustics correlations Christophe in order to determine its acoustic field and to study noise generation mechanisms. The jet streams, and narrow-band spectra with noise measurements carried out during the EU project CoJeN for a coaxial jet

Paris-Sud XI, Université de

193

ANOPP Landing Gear Noise Prediction Comparisons to Model-scale Data  

NASA Technical Reports Server (NTRS)

The NASA Aircraft NOise Prediction Program (ANOPP) includes two methods for computing the noise from landing gear: the "Fink" method and the "Guo" method. Both methods have been predominately validated and used to predict full-scale landing gear noise. The two methods are compared, and their ability to predict the noise for model-scale landing gear is investigated. Predictions are made using both the Fink and Guo methods and compared to measured acoustic data obtained for a high-fidelity, 6.3%-scale, Boeing 777 main landing gear. A process is developed by which full-scale predictions can be scaled to compare with model-scale data. The measurements were obtained in the NASA Langley Quiet Flow Facility for a range of Mach numbers at a large number of observer polar (flyover) and azimuthal (sideline) observer angles. Spectra and contours of the measured sound pressure levels as a function of polar and azimuthal angle characterize the directivity of landing gear noise. Comparisons of predicted noise spectra and contours from each ANOPP method are made. Both methods predict comparable amplitudes and trends for the flyover locations, but deviate at the sideline locations. Neither method fully captures the measured noise directivity. The availability of these measured data provides the opportunity to further understand and advance noise prediction capabilities, particularly for noise directivity.

Burley, Casey L.; Brooks, Thomas F.; Humphreys, William M., Jr.; Rawls, John W., Jr.

2007-01-01

194

Cyclostationary spectral analysis for the measurement and prediction of wind turbine swishing noise  

NASA Astrophysics Data System (ADS)

This paper introduces cyclostationary spectral analysis as a new approach to analyzing and predicting the aerodynamic noise generated by wind turbines. This method is able to reveal new insights into the periodic character of the noise signal and is therefore ideally suited to the study of wind turbine noise. A new formulation is presented for the time variation of the noise spectrum due to wind turbines thereby providing insight into the character of the periodic variation in noise referred to as 'swishing'. The character and mechanism of swishing noise is analyzed in detail.

Cheong, Cheolung; Joseph, Phillip

2014-07-01

195

Maneuvering Rotorcraft Noise Prediction: A New Code for a New Problem  

NASA Technical Reports Server (NTRS)

This paper presents the unique aspects of the development of an entirely new maneuver noise prediction code called PSU-WOPWOP. The main focus of the code is the aeroacoustic aspects of the maneuver noise problem, when the aeromechanical input data are provided (namely aircraft and blade motion, blade airloads). The PSU-WOPWOP noise prediction capability was developed for rotors in steady and transient maneuvering flight. Featuring an object-oriented design, the code allows great flexibility for complex rotor configuration and motion (including multiple rotors and full aircraft motion). The relative locations and number of hinges, flexures, and body motions can be arbitrarily specified to match the any specific rotorcraft. An analysis of algorithm efficiency is performed for maneuver noise prediction along with a description of the tradeoffs made specifically for the maneuvering noise problem. Noise predictions for the main rotor of a rotorcraft in steady descent, transient (arrested) descent, hover and a mild "pop-up" maneuver are demonstrated.

Brentner, Kenneth S.; Bres, Guillaume A.; Perez, Guillaume; Jones, Henry E.

2002-01-01

196

New Computational Methods for the Prediction and Analysis of Helicopter Noise  

NASA Technical Reports Server (NTRS)

This paper describes several new methods to predict and analyze rotorcraft noise. These methods are: 1) a combined computational fluid dynamics and Kirchhoff scheme for far-field noise predictions, 2) parallel computer implementation of the Kirchhoff integrations, 3) audio and visual rendering of the computed acoustic predictions over large far-field regions, and 4) acoustic tracebacks to the Kirchhoff surface to pinpoint the sources of the rotor noise. The paper describes each method and presents sample results for three test cases. The first case consists of in-plane high-speed impulsive noise and the other two cases show idealized parallel and oblique blade-vortex interactions. The computed results show good agreement with available experimental data but convey much more information about the far-field noise propagation. When taken together, these new analysis methods exploit the power of new computer technologies and offer the potential to significantly improve our prediction and understanding of rotorcraft noise.

Strawn, Roger C.; Oliker, Leonid; Biswas, Rupak

1996-01-01

197

RETRACTED: Flap side edge noise modeling and prediction  

NASA Astrophysics Data System (ADS)

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy).This article has been retracted at the request of the first author because of the overlap with previously published papers. The first author takes full responsibility and sincerely apologizes for the error made.This article has been retracted at the request of the Editor-in-Chief.The article duplicates significant parts of an earlier paper by the same author, published in AIAA (Y.P. Guo, Aircraft flap side edge noise modeling and prediction. American Institute of Aeronautics and Astronautics, (2011), 10.2514/6.2011-2731). Prior to republication, conference papers should be comprehensively extended, and re-use of any data should be appropriately cited. As such this article represents a severe abuse of the scientific publishing system. The scientific community takes a very strong view on this matter and apologies are offered to readers of the journal that this was not detected during the submission process.

Guo, Yueping

2013-08-01

198

Validation of Aircraft Noise Prediction Models at Low Levels of Exposure  

NASA Technical Reports Server (NTRS)

Aircraft noise measurements were made at Denver International Airport for a period of four weeks. Detailed operational information was provided by airline operators which enabled noise levels to be predicted using the FAA's Integrated Noise Model. Several thrust prediction techniques were evaluated. Measured sound exposure levels for departure operations were found to be 4 to 10 dB higher than predicted, depending on the thrust prediction technique employed. Differences between measured and predicted levels are shown to be related to atmospheric conditions present at the aircraft altitude.

Page, Juliet A.; Hobbs, Christopher M.; Plotkin, Kenneth J.; Stusnick, Eric; Shepherd, Kevin P. (Technical Monitor)

2000-01-01

199

Source Noise Modeling Efforts for Fan Noise in NASA Research Programs  

NASA Technical Reports Server (NTRS)

There has been considerable progress made in fan noise prediction over the past 15 years. NASA has conducted and sponsored research that has improved both tone and broadband fan noise prediction methods. This presentation highlights progress in these areas with emphasis on rotor/stator interaction noise sources. Tone noise predictions are presented for an advanced prediction code called "LINFLUX". Comparisons with data are" included for individual fan duct modes. There has also been considerable work developing new fan broadband noise prediction codes and validation data from wind tunnel model tests. Results from several code validation exercises are presented that show improvement of predicted sound power levels. A summary is included with recommendations for future work.

Huff, Dennis L.

2006-01-01

200

Auditory Brainstem Response to Complex Sounds Predicts Self-Reported Speech-in-Noise Performance  

ERIC Educational Resources Information Center

Purpose: To compare the ability of the auditory brainstem response to complex sounds (cABR) to predict subjective ratings of speech understanding in noise on the Speech, Spatial, and Qualities of Hearing Scale (SSQ; Gatehouse & Noble, 2004) relative to the predictive ability of the Quick Speech-in-Noise test (QuickSIN; Killion, Niquette,…

Anderson, Samira; Parbery-Clark, Alexandra; White-Schwoch, Travis; Kraus, Nina

2013-01-01

201

Accurate and Efficient Prediction of Acoustical Performance of Noise Barriers against Transport Noise Pollution  

Microsoft Academic Search

This paper aims to establish a framework for effective design of noise barriers based on two key noise abatement mechanisms\\u000a — acoustical wave diffraction and active wave energy dissipation. Both mechanisms are evaluated for noise barriers of an optimal\\u000a design using an integrated approach based on a novel acoustical wave propagator technique, numerical simulations of wave interaction\\u000a with the barriers,

S. Z. Peng; L. Cheng; Y. S. Choy; H. M. Sun

202

Noise Prediction in Urban Traffic by a Neural Approach  

Microsoft Academic Search

The aim of this paper is to determine functional relationships between the road traffic noise and some physical parameters. Should this goal achieved, it is possible to modify the causes of traffic noise, in order to sensibly reduce it. Correlations are usually derived trough multiple regression analysis. In this paper an alternative solution based on the use of a neural

G. Cammarata; Salvatore Cavalieri; A. Fichera; L. Marletta

1993-01-01

203

23 CFR 772.9 - Traffic noise prediction.  

Code of Federal Regulations, 2013 CFR

...in part 7 of title 49, CFR. These documents are also available on the FHWA's Traffic Noise Model Web site at the following URL: http://www.fhwa.dot.gov/environment/noise/index.htm. (b) Average pavement type shall be used in...

2013-04-01

204

23 CFR 772.9 - Traffic noise prediction.  

...in part 7 of title 49, CFR. These documents are also available on the FHWA's Traffic Noise Model Web site at the following URL: http://www.fhwa.dot.gov/environment/noise/index.htm. (b) Average pavement type shall be used in...

2014-04-01

205

23 CFR 772.9 - Traffic noise prediction.  

Code of Federal Regulations, 2012 CFR

...in part 7 of title 49, CFR. These documents are also available on the FHWA's Traffic Noise Model Web site at the following URL: http://www.fhwa.dot.gov/environment/noise/index.htm. (b) Average pavement type shall be used in...

2012-04-01

206

THE PREDICTION OF AIRFRAME NOISE AND COMPARISON WITH EXPERIMENT  

Microsoft Academic Search

The success of the high bypass ratio turbofan engine in reducing the external noise of civil transport aircraft at take-off and landing, while improving the economics of air travel, has opened up the debate as to how much further it will be possible to reduce aircraft noise by the introduction of new aircraft or existing aircraft retrofitted with new engines.

G. M. LILLEY

2001-01-01

207

The Prediction of Airframe Noise and Comparison with Experiment  

Microsoft Academic Search

The success of the high bypass ratio turbofan engine in reducing the external noise of civil transport aircraft at take-off and landing, while improving the economics of air travel, has opened up the debate as to how much further it will be possible to reduce aircraft noise by the introduction of new aircraft or existing aircraft retrofitted with new engines.

G. M. Lilley

2001-01-01

208

Evaluation and prediction of blade-passing frequency noise generated by a centrifugal blower  

SciTech Connect

The blade-passing frequency noise, abbreviated to BPF noise, of a low-specific-speed centrifugal blower is analyzed by separating the frequency response of the transmission passage and the intensity of the noise source. Frequency response has previously been evaluated by the authors using a one-dimensional linear wave model, and the results have agreed well with the experimental response in a practical range of the blower speed. In the present study, the intensity of the noise source is estimated by introducing the quasi-steady model of the blade wake impingement on the scroll surface. The effective location of the noise source is determined by analyzing the cross-correlation between measured data of the blower suction noise and pressure fluctuation on the scroll surface. Then, the surface density distribution of a dipole noise source is determined from pressure fluctuations expressed in terms of quasi-steady dynamic pressure of the traveling blade wake. Finally, the free-field noise level is predicted by integrating the density spectrum of the noise source over the effective source area. The sound pressure level of the blower suction noise is easily predicted by multiplying the free-field noise level by the frequency-response characteristics of the noise transmission passage.

Ohta, Y.; Outa, E.; Tajima, K. [Waseda Univ., Tokyo (Japan). Dept. of Mechanical Engineering

1996-07-01

209

Image discrimination models predict detection in fixed but not random noise.  

PubMed

By means of a two-interval forced-choice procedure, contrast detection thresholds for an aircraft positioned on a simulated airport runway scene were measured with fixed and random white-noise masks. The term fixed noise refers to a constant, or unchanging, noise pattern for each stimulus presentation. The random noise was either the same or different in the two intervals. Contrary to simple image discrimination model predictions, the same random noise condition produced greater masking than the fixed noise. This suggests that observers seem unable to hold a new noisy image for comparison. Also, performance appeared limited by internal process variability rather than by external noise variability, since similar masking was obtained for both random noise types. PMID:9291614

Ahumada, A J; Beard, B L

1997-09-01

210

Simultaneous effects of sinusoidal whole body vibration and broadband noise on TTS2's and R-wave amplitudes in men at two different dry bulb temperatures.  

PubMed

The aim of this study was to investigate the temporary hearing threshold shift (TTS2) and R-wave amplitudes in eleven healthy males when they were exposed to paired sinusoidal whole body (Z-axis) vibration (5 Hz--2.12 m/s2) and stable broadband A-weighted white noise at dry bulb temperatures of 20 degrees C and 30 degrees C. The intensity of noise in the exposure combinations was 75, 85 and 95 dB(A). The total number of tests was 66, and they were carried out in an exposure chamber. The subjects were dressed in standard clothing, and carried out simple tasks using a choice reaction time device during the test. According to the results, the means of the TTS2 values were usually higher at the dry bulb temperature of 30 degrees C than at 20 degrees C. Hearing threshold shifts were the greatest at frequencies of 4 and 6 kHz, and the smallest at 8 kHz. The more intense the noise in the paired combination of noise and vibration, the clearer the tendency for an increase in the ambient temperature to accelerate the increase in the hearing threshold. The effect of the ambient temperature on the temporary hearing threshold shifts also appeared to be slightly stronger during successive exposure cycles. Changes in the values for the R-wave amplitudes seemed to be connected with those in the hearing threshold. The decrease in the R-wave amplitude was connected to the increase in the TTS2 values, especially when the subjects were simultaneously exposed to a 95 dB(A) noise and whole body vibration at the dry bulb temperature of 30 degrees C. This implies that an increase in the ambient temperature intensifies cardiovascular disturbances in the body, which accelerate the development of functional disturbance in the inner ear. PMID:6862642

Manninen, O

1983-01-01

211

On INM's Use of Corrected Net Thrust for the Prediction of Jet Aircraft Noise  

NASA Technical Reports Server (NTRS)

The Federal Aviation Administration s (FAA) Integrated Noise Model (INM) employs a prediction methodology that relies on corrected net thrust as the sole correlating parameter between aircraft and engine operating states and aircraft noise. Thus aircraft noise measured for one set of atmospheric and aircraft operating conditions is assumed to be applicable to all other conditions as long as the corrected net thrust remains constant. This hypothesis is investigated under two primary assumptions: (1) the sound field generated by the aircraft is dominated by jet noise, and (2) the sound field generated by the jet flow is adequately described by Lighthill s theory of noise generated by turbulence.

McAninch, Gerry L.; Shepherd, Kevin P.

2011-01-01

212

Interior noise considerations for advanced high-speed turboprop aircraft  

NASA Technical Reports Server (NTRS)

This paper describes recent research on noise generated by high-speed propellers, on noise transmission through acoustically treated aircraft sidewalls and on subjective response to simulated turboprop noise. Propeller noise discussion focuses on theoretical prediction methods for complex blade shapes designed for low noise at Mach = 0.8 flight and on comparisons with experimental test results. Noise transmission experiments using a 168 cm. diameter aircraft fuselage model and scaled heavy-double-wall treatments indicate that the treatments perform well and that the predictions are usually conservative. Studies of subjective comfort response in an anechoic environment are described for noise signatures having combinations of broadband and propeller-type tone components.

Mixson, J. S.; Farassat, F.; Leatherwood, J. D.; Prydz, R.; Revell, J. D.

1982-01-01

213

Using the short-time speech transmission index to predict speech reception thresholds in fluctuating noise.  

PubMed

The Speech Transmission Index (STI) predicts the intelligibility of speech degraded by noise and reverberation. Recently, Payton and Shrestha [J. Acoust. Soc. Am. 134, 3818-3827 (2013)] reported on the ability of a short-time speech-based STI (ssSTI) to predict the intelligibility of speech in the presence of fluctuating noise using analysis windows shorter than 1 s. They found the ssSTI highly correlated with theoretical STI calculations using windows as short as 0.3 s. In the current work, extended versions of the ssSTI were investigated for their ability to improve speech intelligibility prediction in the presence of fluctuating noise; a condition for which the long-term STI incorrectly predicts the same intelligibility as for stationary noise. No STI metric predicts a normal-hearing listener's improved ability to perceive speech in the presence of fluctuating noise as compared to stationary noise at the same signal-to-noise ratio. The investigated technique used window lengths that varied with octave band, based on human auditory temporal resolution as in the Extended Speech Intelligibility Index [Rhebergen and Versfeld, J. Acoust. Soc. Am. 117, 2181-2192 (2005)]. An extended sSTI using speech-shaped noise instead of speech as a probe predicted published speech reception thresholds for a variety of conditions. PMID:25235329

Ferreira, Matthew; Payton, Karen

2014-04-01

214

Comparison of Noise Source Localization Data with Flow Field Data Obtained in Cold Supersonic Jets and Implications Regarding Broadband Shock Noise  

NASA Technical Reports Server (NTRS)

Phased array noise source localization have been compared with 2 types of flow field data (BOS and PIV). The data show that: 1) the higher frequency noise in a BBSN hump is generated further downstream than the lower frequency noise. This is due to a) the shock spacing decreasing and b) the turbulent structure size increasing with distance downstream. 2) BBSN can be created by very weak shocks. 3) BBSN is not created by the strong shocks just downstream of the nozzle because the turbulent structures have not grown large enough to match the shock spacing. 4) The point in the flow where the shock spacing equals the average size of the turbulent structures is a hot spot for shock noise. 5) Some of the shocks responsible for producing the first hump also produce the second hump.

Podboy, Gary; Wernet, Mark; Clem, Michelle; Fagan, Amy

2013-01-01

215

Validation of finite element and boundary element methods for predicting structural vibration and radiated noise  

NASA Technical Reports Server (NTRS)

Analytical and experimental validation of methods to predict structural vibration and radiated noise are presented. A rectangular box excited by a mechanical shaker was used as a vibrating structure. Combined finite element method (FEM) and boundary element method (BEM) models of the apparatus were used to predict the noise radiated from the box. The FEM was used to predict the vibration, and the surface vibration was used as input to the BEM to predict the sound intensity and sound power. Vibration predicted by the FEM model was validated by experimental modal analysis. Noise predicted by the BEM was validated by sound intensity measurements. Three types of results are presented for the total radiated sound power: (1) sound power predicted by the BEM modeling using vibration data measured on the surface of the box; (2) sound power predicted by the FEM/BEM model; and (3) sound power measured by a sound intensity scan. The sound power predicted from the BEM model using measured vibration data yields an excellent prediction of radiated noise. The sound power predicted by the combined FEM/BEM model also gives a good prediction of radiated noise except for a shift of the natural frequencies that are due to limitations in the FEM model.

Seybert, A. F.; Wu, X. F.; Oswald, Fred B.

1992-01-01

216

An Integrated RANS-PSE-Wave Packet Tool for the Prediction of Subsonic and Supersonic Jet Noise  

E-print Network

An Integrated RANS-PSE-Wave Packet Tool for the Prediction of Subsonic and Supersonic Jet Noise for predicting supersonic jet noise, and the development of engine exhaust noise reduction technology such designs are optimal. Arguably, this gap in jet noise modeling capability is an impediment toward achieving

Dabiri, John O.

217

Prediction and Reduction of Noise in Pneumatic Bleed Valves  

NASA Astrophysics Data System (ADS)

This study investigates numerically the fluid mechanics and acoustics of pneumatic bleed valves used in turbofan engines. The goal is to characterized the fundamental processes of noise generation and devise strategies for noise reduction. Three different methods are employed for both analysis and redesign of the bleed valve to reduce noise. The bleed valve noise problem is carefully divided into multiple smaller problems. For large separations and tonal noises, the unsteady Reynolds-Averaged Navier-Stokes (URANS) method is utilized. This method is also applied in the re-designing of the bleed valve geometry. For the bleed valve muffler, which is comprised of perforated plates and a honeycomb, a Reynolds-Averaged Navier-Stokes (RANS) method combined with a simplified acoustic analogy is used. The original muffler design is modified to improve noise attenuation. Finally, for sound scattering through perforated plates, a fully implicit linearized Euler solver is developed. The problem of sound interaction with perforated plates is studied from two perspectives. In the first study the effect of high--speed mean flow is considered and it is shown that at Strouhal numbers of around 0.2-0.25 there is an increase in transmitted incident sound. In the second part, the interaction of holes in two--dimensional perforated plates is investigated using three different configurations. The study demonstrates that the hole interaction has a significant impact on sound attenuation, especially at high frequencies.

Taghavi Nezhad, Shervin

218

Theoretical aspects of supersonic jet noise  

NASA Technical Reports Server (NTRS)

The topics covered include the following: the three components of supersonic jet noise; shock cell structure of imperfectly expanded jets; large turbulence structures/instability waves; supersonic jet noise theory; generation of turbulent mixing noise; comparisons between predicted peak noise frequency and direction of radiation with measurements; Strouhal number of maximum SPL of hot supersonic jets; near field sound pressure level contours; generation of broadband shock associated noise; calculated and measured far field shock noise spectra; generation of screech tones; and calculated and measured Strouhal number of screech tones.

Tam, Christopher K. W.

1992-01-01

219

A new capability for predicting helicopter rotor and propeller noise including the effect of forward motion  

NASA Technical Reports Server (NTRS)

The governing equation and computing technique for the prediction of helicopter rotor and propeller noise are described. The method which gives both the acoustic pressure time history and spectrum of the noise includes the thickness and the loading noise. It was adapted to computers resulting in a new capability in noise prediction by removing many of the restrictions and limitations of previous theories. The capability results from the fact that the theory is developed entirely in the time domain. The formulation and the technique used are not limited to compact sources, steady level flight or to the far-field. In addition, the inputs to the computer program are normally available or are amenable to experimental measurements. This program can be used to study rotor and propeller noise with the aim of minimizing the radiated noise to reduce annoyance to the public. Several examples demonstrating the features and capability of the computer program are presented.

Farassat, F.; Brown, T. J.

1977-01-01

220

Evaluation of ride quality prediction methods for helicopter interior noise and vibration environments  

NASA Technical Reports Server (NTRS)

The results of a simulator study conducted to compare and validate various ride quality prediction methods for use in assessing passenger/crew ride comfort within helicopters are presented. Included are results quantifying 35 helicopter pilots discomfort responses to helicopter interior noise and vibration typical of routine flights, assessment of various ride quality metrics including the NASA ride comfort model, and examination of possible criteria approaches. Results of the study indicated that crew discomfort results from a complex interaction between vibration and interior noise. Overall measures such as weighted or unweighted root-mean-square acceleration level and A-weighted noise level were not good predictors of discomfort. Accurate prediction required a metric incorporating the interactive effects of both noise and vibration. The best metric for predicting crew comfort to the combined noise and vibration environment was the NASA discomfort index.

Leatherwood, J. D.; Clevenson, S. A.; Hollenbaugh, D. D.

1984-01-01

221

Simple method for prediction of aircraft noise contours  

NASA Technical Reports Server (NTRS)

A method for generating noise contours more rapidly and more simply than previously used programs is discussed. The method gives the area, the noise contour, and its extremities for an arbitrarily complex flight path for both takeoffs and landings with relative ease. The analysis reveals the fundamental nature of the contours and how the various factors that influence its size and shape enter into the analysis. It is noted that the effects of ground attenuation and shielding are omitted as they are important only on the initial portion of flight and are highly dependent upon aircraft configuration. However, the analysis shows that these effects could be included. It is emphasized the the single-event contour is an obvious choice for purposes of minimizing noise impact.

Stewart, E. C.; Carson, T. M.

1980-01-01

222

Toward high-fidelity subsonic jet noise prediction using petascale supercomputers  

NASA Astrophysics Data System (ADS)

The field of jet noise has become one of most active areas of research due to increasingly stringent aircraft noise regulations. A petascalable noise prediction tool-set based on the large eddy simulation (LES) technique is designed and implemented to improve the fidelity of subsonic jet noise predictions. Such tools are needed to help drive the design of quieter jets. The focus is to target computational performance and improved noise prediction fidelity through better matching experimental jet conditions and/or inclusion of the nozzle as part of the simulation. A communication-efficient SPIKE solver is used for spatial operations in conjunction with a non-overlapping multi-block topology based on a new concept of superblocks. These two choices have resulted in efficient scalability tested on up to 91,125 processors (or a theoretical speed of ˜1 petaflop/s). Other important optimizations include parallel file I/O and data buffering while gathering the acoustics. The noise from a Mach-0.9, isothermal jet is studied without and with a round nozzle. Production runs with up to first-ever one-billion-point simple-block topology grids without the nozzle and 125-million-point multi-block topology grids with the nozzle are performed. A vortex ring is used to excite the shear layers in the cases without the nozzle. The fine grid simulations with thinner shear layers have predicted higher sideline noise levels caused by the vortex ring and hence, established the need for nozzle inclusion. The problems of the centerline singularity and smaller time step size due to cylindrical grids have been addressed. A new, faster method based on a sinc filter is discussed for the time step issue in cylindrical grids. Two approaches are considered for nozzle inclusion by: 1) fully resolving the boundary layers at a lower Reynolds number; and 2) using a wall model to model the inner layer at the experimental Reynolds number. The wall-modeled cases exhibited numerical instabilities behind the nozzle lip which contaminated the far-field noise data, whereas the wall-resolved cases showed no such problems. The latter cases predicted noise and spectra that are in better agreement with the experiments. Overall, the inclusion of the nozzle as part of the LES is found to improve the noise predictions. Various innovative noise analysis tools have been used to understand the jet noise to a better extent. Lastly, specific guidelines have been suggested to improve jet noise predictions. It is hoped that the predicted noise levels with improved fidelity will help drive the design of quieter nozzles.

Martha, Chandra Sekhar

223

The Uses and Abuses of the Acoustic Analogy in Helicopter Rotor Noise Prediction  

NASA Technical Reports Server (NTRS)

This paper is theoretical in nature and addresses applications of the acoustic analogy in helicopter rotor noise prediction. It is argued that in many instances the acoustic analogy has not been used with care in rotor noise studies. By this it is meant that approximate or inappropriate formulations have been used. By considering various mechanisms of noise generation, such abuses are identified and the remedy is suggested. The mechanisms discussed are thickness, loading, quadrupole, and blade-vortex interaction noise. The quadrupole term of the Ffowcs Williams-Hawkings equation is written in a new form which separates the contributions of regions of high gradients such as shock surfaces. It is shown by order of magnitude studies that such regions are capable of producing noise with the same directivity as the thickness noise. The inclusion of this part of quadrupole sources in current acoustic codes is quite practical. Some of the difficulties with the use of loading noise formulations of the first author in predictions of blade-vortex interaction noise are discussed. It appears that there is a need for development of new theoretical results based on the acoustic analogy in this area. Because of the impulsive character of the blade surface pressure, a time scale of integration different from that used in loading and thickness computations must he used in a computer code for prediction of blade-vortex interaction noise.

Farassat, F.; Brentner, Kenneth S.

1987-01-01

224

Evaluation of Turbulence-Model Performance as Applied to Jet-Noise Prediction  

NASA Technical Reports Server (NTRS)

The accurate prediction of jet noise is possible only if the jet flow field can be predicted accurately. Predictions for the mean velocity and turbulence quantities in the jet flowfield are typically the product of a Reynolds-averaged Navier-Stokes solver coupled with a turbulence model. To evaluate the effectiveness of solvers and turbulence models in predicting those quantities most important to jet noise prediction, two CFD codes and several turbulence models were applied to a jet configuration over a range of jet temperatures for which experimental data is available.

Woodruff, S. L.; Seiner, J. M.; Hussaini, M. Y.; Erlebacher, G.

1998-01-01

225

URBAN NOISE PREDICTS SONG FREQUENCY IN NORTHERN CARDINALS AND AMERICAN ROBINS  

Microsoft Academic Search

We examined the extent to which acoustic noise in urban environments influences song characteristics and singing behaviour of Northern Cardinals Cardinalis cardinalis and American Robins Turdus migratorius. We predicted that, in response to loud noise, birds would improve signal transmission by (1) increasing singing rate and (2) adjusting song characteristics such as pitch and length. From May—July 2006, 42 cardinals

KERRI D. SEGER-FULLAM; AMANDA D. RODEWALD; JILL A. SOHA

2011-01-01

226

Parabolized stability equation models for predicting large-scale mixing noise of turbulent round jets  

E-print Network

speed jets remain challenging and computationally expensive. On the other hand, numerical jet noiseParabolized stability equation models for predicting large-scale mixing noise of turbulent round jets D. Rodr´iguez1 , A. Samanta1 , A. V. G. Cavalieri2 , T. Colonius1§ and P. Jordan2¶ 1 Department

Colonius, Tim

227

Impact of prediction accuracy on costs - noise technology applications in helicopters  

Microsoft Academic Search

This study is an extension of the work reported in AD-A083 935, and considers the effect which uncertainties in the prediction and measurement of helicopter noise have on the development and operating costs. Although the number of helicopters studied is too small to permit generally applicable conclusions, the following are the primary results: (1) the Effective Perceived Noise (EPN) Levels

R. H. Spencer; H. Sternfeld Jr.

1981-01-01

228

Design of the Next Generation Aircraft Noise Prediction Program: ANOPP2  

NASA Technical Reports Server (NTRS)

The requirements, constraints, and design of NASA's next generation Aircraft NOise Prediction Program (ANOPP2) are introduced. Similar to its predecessor (ANOPP), ANOPP2 provides the U.S. Government with an independent aircraft system noise prediction capability that can be used as a stand-alone program or within larger trade studies that include performance, emissions, and fuel burn. The ANOPP2 framework is designed to facilitate the combination of acoustic approaches of varying fidelity for the analysis of noise from conventional and unconventional aircraft. ANOPP2 integrates noise prediction and propagation methods, including those found in ANOPP, into a unified system that is compatible for use within general aircraft analysis software. The design of the system is described in terms of its functionality and capability to perform predictions accounting for distributed sources, installation effects, and propagation through a non-uniform atmosphere including refraction and the influence of terrain. The philosophy of mixed fidelity noise prediction through the use of nested Ffowcs Williams and Hawkings surfaces is presented and specific issues associated with its implementation are identified. Demonstrations for a conventional twin-aisle and an unconventional hybrid wing body aircraft configuration are presented to show the feasibility and capabilities of the system. Isolated model-scale jet noise predictions are also presented using high-fidelity and reduced order models, further demonstrating ANOPP2's ability to provide predictions for model-scale test configurations.

Lopes, Leonard V., Dr.; Burley, Casey L.

2011-01-01

229

Prediction of jet noise in flight from static tests  

Microsoft Academic Search

The sound intensity of jet noise from aircraft in flight is derived in a coordinate system fixed to the jet engine. For this reason a convected form of the Lighthill equation is solved, with special care taken of jet temperature effects. Under certain assumptions and approximations, the in-flight and static sound intensities are related in a simple manner. Thus the

A. Michalke; U. Michel

1979-01-01

230

Jet noise prediction using the Lighthill acoustic analogy  

Microsoft Academic Search

A jet noise source model based on the Lighthill acoustic analogy is presented. Although much of the theory used is well known, a new feature of the model is the inclusion of frequency dependence for the time and length scales used in the turbulence two-point correlation function. It is found that allowing for this experimentally observed dependence markedly improves the

R. H Self

2004-01-01

231

Prediction of XV-15 tilt rotor discrete frequency aeroacoustic noise with WOPWOP  

NASA Technical Reports Server (NTRS)

The results, methodology, and conclusions of noise prediction calculations carried out to study several possible discrete frequency harmonic noise mechanisms of the XV-15 Tilt Rotor Aircraft in hover and helicopter mode forward flight are presented. The mechanisms studied were thickness and loading noise. In particular, the loading noise caused by flow separation and the fountain/ground plane effect were predicted with calculations made using WOPWOP, a noise prediction program developed by NASA Langley. The methodology was to model the geometry and aerodynamics of the XV-15 rotor blades in hover and steady level flight and then create corresponding FORTRAN subroutines which were used an input for WOPWOP. The models are described and the simplifying assumptions made in creating them are evaluated, and the results of the computations are presented. The computations lead to the following conclusions: The fountain/ground plane effect is an important source of aerodynamic noise for the XV-15 in hover. Unsteady flow separation from the airfoil passing through the fountain at high angles of attack significantly affects the predicted sound spectra and may be an important noise mechanism for the XV-15 in hover mode. The various models developed did not predict the sound spectra in helicopter forward flight. The experimental spectra indicate the presence of blade vortex interactions which were not modeled in these calculations. A need for further study and development of more accurate aerodynamic models, including unsteady stall in hover and blade vortex interactions in forward flight.

Coffen, Charles D.; George, Albert R.

1990-01-01

232

Measured and predicted noise of the AVCO-Lycoming YF-102 turbofan engine  

NASA Technical Reports Server (NTRS)

Acoustic testing of the AVCO-Lycoming YF-102 turbofan engine was done on a static test stand at Lewis Research Center in support of the Quiet Short-Haul Research Aircraft (QSRA) acoustic design. Overall noise levels are dominated by the fan noise emanating from the exhaust duct, except at high power settings when combination tones are generated in the fan inlet. Component noise levels, calculated by noise prediction methods developed at Lewis Research Center for the ANOP program, are in reasonable agreement with the measured results. Far-field microphones placed at ground level were found superior to those at engine centerline height, even at high frequencies.

Clark, B. J.; Mcardle, J. G.; Homyak, L.

1979-01-01

233

Development of a traffic noise prediction model for an urban environment.  

PubMed

The objective of this study is to develop a traffic noise model under diverse traffic conditions in metropolitan cities. The model has been developed to calculate equivalent traffic noise based on four input variables i.e. equivalent traffic flow (Q e ), equivalent vehicle speed (S e ) and distance (d) and honking (h). The traffic data is collected and statistically analyzed in three different cases for 15-min during morning and evening rush hours. Case I represents congested traffic where equivalent vehicle speed is <30 km/h while case II represents free-flowing traffic where equivalent vehicle speed is >30 km/h and case III represents calm traffic where no honking is recorded. The noise model showed better results than earlier developed noise model for Indian traffic conditions. A comparative assessment between present and earlier developed noise model has also been presented in the study. The model is validated with measured noise levels and the correlation coefficients between measured and predicted noise levels were found to be 0.75, 0.83 and 0.86 for case I, II and III respectively. The noise model performs reasonably well under different traffic conditions and could be implemented for traffic noise prediction at other region as well. PMID:24583682

Sharma, Asheesh; Bodhe, G L; Schimak, G

2014-01-01

234

Landing-gear noise prediction using high-order finite difference schemes  

NASA Astrophysics Data System (ADS)

Aerodynamic noise from a generic two-wheel landing-gear model is predicted by a CFD/FW-H hybrid approach. The unsteady flow-field is computed using a compressible Navier-Stokes solver based on high-order finite difference schemes and a fully structured grid. The calculated time history of the surface pressure data is used in an FW-H solver to predict the far-field noise levels. Both aerodynamic and aeroacoustic results are compared to wind tunnel measurements and are found to be in good agreement. The far-field noise was found to vary with the 6th power of the free-stream velocity. Individual contributions from three components, i.e. wheels, axle and strut of the landing-gear model are also investigated to identify the relative contribution to the total noise by each component. It is found that the wheels are the dominant noise source in general. Strong vortex shedding from the axle is the second major contributor to landing-gear noise. This work is part of Airbus LAnding Gear nOise database for CAA validatiON (LAGOON) program with the general purpose of evaluating current CFD/CAA and experimental techniques for airframe noise prediction.

Liu, Wen; Wook Kim, Jae; Zhang, Xin; Angland, David; Caruelle, Bastien

2013-07-01

235

Broadband and Low Phase Noise VCO Using Tunable Metamaterial Transmission Line Based on Varactor-Loaded Split-Ring Resonator  

Microsoft Academic Search

A voltage-controlled oscillator (VCO) using tunable metamaterial transmission line based on varactor-loaded split-ring resonator (VLSRR) is presented to enhance the tuning range and reduce the phase noise. It is demonstrated that VLSRR coupled to microstrip line can lead to metamaterial transmission line with tuning capability. The negative effective permeability is provided by VLSRR in a narrow band above the resonant

Jaewon Choi; Chulhun Seo

2007-01-01

236

Coherent backscattering noise in a photonic-bandgap fiber optic gyroscope  

Microsoft Academic Search

Numerical simulations predict that the coherent backscattering noise of a fiber optic gyroscope (FOG) interrogated with a laser decreases when the laser's coherence length exceeds the length of the fiber loop. With a sufficiently coherent laser, this noise drops below the excess noise of the same FOG probed with broadband light. This new principle is paramount for the air-core FOG,

Michel J. F. Digonnet; Seth W. Lloyd; Shanhui Fan

2009-01-01

237

Novel Methods for Predicting Photometric Redshifts from Broadband Photometry Using Virtual Sensors  

NASA Astrophysics Data System (ADS)

We calculate photometric redshifts from the Sloan Digital Sky Survey Main Galaxy Sample, the Galaxy Evolution Explorer All Sky Survey, and the Two Micron All Sky Survey using two new training-set methods. We utilize the broadband photometry from the three surveys alongside Sloan Digital Sky Survey measures of photometric quality and galaxy morphology. Our first training-set method draws from the theory of ensemble learning while the second employs Gaussian process regression, both of which allow for the estimation of redshift along with a measure of uncertainty in the estimation. The Gaussian process models the data very effectively with small training samples of approximately 1000 points or less. These two methods are compared to a well-known artificial neural network training-set method and to simple linear and quadratic regression. We also demonstrate the need to provide confidence bands on the error estimation made by both classes of models. Our results indicate that variations due to the optimization procedure used for almost all neural networks, combined with the variations due to the data sample, can produce models with variations in accuracy that span an order of magnitude. A key contribution of this paper is to quantify the variability in the quality of results as a function of model and training sample. We show how simply choosing the ``best'' model given a data set and model class can produce misleading results.

Way, M. J.; Srivastava, A. N.

2006-08-01

238

The Acoustic Analogy: A Powerful Tool in Aeroacoustics with Emphasis on Jet Noise Prediction  

NASA Technical Reports Server (NTRS)

The acoustic analogy introduced by Lighthill to study jet noise is now over 50 years old. In the present paper, Lighthill s Acoustic Analogy is revisited together with a brief evaluation of the state-of-the-art of the subject and an exploration of the possibility of further improvements in jet noise prediction from analytical methods, computational fluid dynamics (CFD) predictions, and measurement techniques. Experimental Particle Image Velocimetry (PIV) data is used both to evaluate turbulent statistics from Reynolds-averaged Navier-Stokes (RANS) CFD and to propose correlation models for the Lighthill stress tensor. The NASA Langley Jet3D code is used to study the effect of these models on jet noise prediction. From the analytical investigation, a retarded time correction is shown that improves, by approximately 8 dB, the over-prediction of aft-arc jet noise by Jet3D. In experimental investigation, the PIV data agree well with the CFD mean flow predictions, with room for improvement in Reynolds stress predictions. Initial modifications, suggested by the PIV data, to the form of the Jet3D correlation model showed no noticeable improvements in jet noise prediction.

Farassat, F.; Doty, Michael J.; Hunter, Craig A.

2004-01-01

239

Development and Validation of a Multidisciplinary Tool for Accurate and Efficient Rotorcraft Noise Prediction (MUTE)  

NASA Technical Reports Server (NTRS)

A physics-based, systematically coupled, multidisciplinary prediction tool (MUTE) for rotorcraft noise was developed and validated with a wide range of flight configurations and conditions. MUTE is an aggregation of multidisciplinary computational tools that accurately and efficiently model the physics of the source of rotorcraft noise, and predict the noise at far-field observer locations. It uses systematic coupling approaches among multiple disciplines including Computational Fluid Dynamics (CFD), Computational Structural Dynamics (CSD), and high fidelity acoustics. Within MUTE, advanced high-order CFD tools are used around the rotor blade to predict the transonic flow (shock wave) effects, which generate the high-speed impulsive noise. Predictions of the blade-vortex interaction noise in low speed flight are also improved by using the Particle Vortex Transport Method (PVTM), which preserves the wake flow details required for blade/wake and fuselage/wake interactions. The accuracy of the source noise prediction is further improved by utilizing a coupling approach between CFD and CSD, so that the effects of key structural dynamics, elastic blade deformations, and trim solutions are correctly represented in the analysis. The blade loading information and/or the flow field parameters around the rotor blade predicted by the CFD/CSD coupling approach are used to predict the acoustic signatures at far-field observer locations with a high-fidelity noise propagation code (WOPWOP3). The predicted results from the MUTE tool for rotor blade aerodynamic loading and far-field acoustic signatures are compared and validated with a variation of experimental data sets, such as UH60-A data, DNW test data and HART II test data.

Liu, Yi; Anusonti-Inthra, Phuriwat; Diskin, Boris

2011-01-01

240

An empirical method for predicting the mixing noise levels of subsonic circular and coaxial jets  

NASA Technical Reports Server (NTRS)

An empirical method for predicting the static free field source noise levels of subsonic circular and coaxial jet flow streams is presented. The method was developed from an extensive data base of 817 jet tests obtained from five different government and industry sources in three nations. The prediction method defines the jet noise in terms of four components which are overall power level, power spectrum level, directivity index, and relative spectrum level. The values of these noise level components are defined on a grid consisting of seven frequency parameter values (Strouhal numbers) and seven directivity angles. The value of the noise level at each of these grid points is called a noise level coordinate and was defined as a function of five jet exhaust flow state parameters which are equivalent jet velocity, equivalent jet total temperature, the velocity ratio (outer stream to inner stream), temperature ratio, and area ratio. The functions were obtained by curve fitting in a least squares sense the noise level coordinates from the data base in a five dimensional flow state space using a third order Taylor series. The noise level coordinates define the component noise levels for all frequencies and directivities through a bicubic spline function.

Russell, J. W.

1984-01-01

241

Noise and randomlike behavior of perceptrons: Theory and applicationto protein structure prediction  

NASA Astrophysics Data System (ADS)

In the first part of this paper we study the performance of a single-layer perceptron that is expected to classify patterns into classes in the case where the mapping to be learned is corrupted by noise. Extending previous results concerning the statistical behavior of perceptrons, we distinguish two mutually exclusive kinds of noise (I noise and R noise) and study their effect on the statistical information that can be drawn from the output. In the presence of I noise, the learning stage results in the convergence of the output to the probabilities that the input occurs in each class. R noise, on the contrary, perturbs the learning of probabilities to the extent that the performance of the perceptron deteriorates and the network becomes equivalent to a random predictor. We derive an analytical expression for the efficiency of classification of inputs affected by strong R noise. We argue that, from the standpoint of the efficiency score, the network is equivalent to a device performing biased random flights in the space of the weights, which are ruled by the statistical information stored by the network during the learning stage. The second part of the paper is devoted to the application of our model to the prediction of protein secondary structures where one has to deal with the effects of R noise. Our results are shown to be consistent with data drawn from experiments and simulations of the folding process. In particular, the existence of coding and noncoding traits of the protein is properly rationalized in terms of R-noise intensity. In addition, our model provides a justification of the seeming existence of a relationship between the prediction efficiency and the amount of R noise in the sequence-to-structure mapping. Finally, we define an entropylike parameter that is useful as a measure of R noise.

Compiani, M.; Fariselli, P.; Casadio, R.

1997-06-01

242

Noise-immune cavity-enhanced optical frequency comb spectroscopy: A sensitive technique for high-resolution broadband molecular detection  

E-print Network

Noise-immune cavity-enhanced optical frequency comb spectroscopy (NICE-OFCS) is a recently developed technique that utilizes phase modulation to obtain immunity to frequency-to-amplitude noise conversion by the cavity modes and yields high absorption sensitivity over a broad spectral range. We describe the principles of the technique and discuss possible comb-cavity matching solutions. We present a theoretical description of NICE-OFCS signals detected with a Fourier transform spectrometer (FTS), and validate the model by comparing it to experimental CO2 spectra around 1575 nm. Our system is based on an Er:fiber femtosecond laser locked to a cavity and phase-modulated at a frequency equal to a multiple of the cavity free spectral range (FSR). The NICE-OFCS signal is detected by a fast-scanning FTS equipped with a high-bandwidth commercial detector. We demonstrate a simple method of passive locking of the modulation frequency to the cavity FSR that significantly improves the long term stability of the system, a...

Khodabakhsh, Amir; Foltynowicz, Aleksandra

2014-01-01

243

A Noise Level Prediction Method Based on Electro-Mechanical Frequency Response Function for Capacitors  

PubMed Central

The capacitors in high-voltage direct-current (HVDC) converter stations radiate a lot of audible noise which can reach higher than 100 dB. The existing noise level prediction methods are not satisfying enough. In this paper, a new noise level prediction method is proposed based on a frequency response function considering both electrical and mechanical characteristics of capacitors. The electro-mechanical frequency response function (EMFRF) is defined as the frequency domain quotient of the vibration response and the squared capacitor voltage, and it is obtained from impulse current experiment. Under given excitations, the vibration response of the capacitor tank is the product of EMFRF and the square of the given capacitor voltage in frequency domain, and the radiated audible noise is calculated by structure acoustic coupling formulas. The noise level under the same excitations is also measured in laboratory, and the results are compared with the prediction. The comparison proves that the noise prediction method is effective. PMID:24349105

Zhu, Lingyu; Ji, Shengchang; Shen, Qi; Liu, Yuan; Li, Jinyu; Liu, Hao

2013-01-01

244

Wavelet Transform Noise Elimination and Its Application in City Heating Load Prediction  

E-print Network

In this paper, the real-time measuring data with noise undergo wavelet transformation. With the treated data and an internal time-delay Elman network, city heating supply predictive models are established and short-term real-time predictions...

Jiang, Y.; Jun, X.; Wei, B.

2006-01-01

245

Prediction of noise field of a propfan at angle of attack  

NASA Technical Reports Server (NTRS)

A method for predicting the noise field of a propfan operating at an angle of attack to the oncoming flow is presented. The method takes advantage of the high-blade-count of the advanced propeller designs to provide an accurate and efficient formula for predicting their noise field. The formula, which is written in terms of the Airy function and its derivative, provides a very attractive alternative to the use of numerical integration. A preliminary comparison shows rather favorable agreement between the predictions from the present method and the experimental data.

Envia, Edmane

1991-01-01

246

Curved Duct Noise Prediction Using the Fast Scattering Code  

NASA Technical Reports Server (NTRS)

Results of a study to validate the Fast Scattering Code (FSC) as a duct noise predictor, including the effects of curvature, finite impedance on the walls, and uniform background flow, are presented in this paper. Infinite duct theory was used to generate the modal content of the sound propagating within the duct. Liner effects were incorporated via a sound absorbing boundary condition on the scattering surfaces. Simulations for a rectangular duct of constant cross-sectional area have been compared to analytical solutions and experimental data. Comparisons with analytical results indicate that the code can properly calculate a given dominant mode for hardwall surfaces. Simulated acoustic behavior in the presence of lined walls (using hardwall duct modes as incident sound) is consistent with expected trends. Duct curvature was found to enhance weaker modes and reduce pressure amplitude. Agreement between simulated and experimental results for a straight duct with hard walls (no flow) was excellent.

Dunn, M. H.; Tinetti, Ana F.; Farassat, F.

2007-01-01

247

Noise  

Microsoft Academic Search

The proliferation of DNA sequence data has generated a concern about the effects of “noise” on phylogeny reconstruction. This concern has led to various recommendations for weighting schemes and for separating data types prior to analysis. A new technique is explored to examine directly how noise influences the stability of parsimony reconstruction. By appending purely random characters onto a matrix

John W Wenzel; Mark E Siddall

1999-01-01

248

Noise and randomlike behavior in perceptrons: theory and application to protein structure prediction  

NASA Astrophysics Data System (ADS)

In this paper we study the effective behavior of a single-layer perceptron that is forced to learn a noisy mapping (e.g. associations of patterns with classes). The effect of different kinds of noise on the output of the network is discussed as a function of the noise intensity. It is argued that noise induces a random-like component in the overall behavior of the perceptron which we describe in terms of independent biased random flights in the space of the weights. These random processes (one for each class) are ruled by probability distributions specified by the weights themselves. Our model is applied to the real world application of the prediction of protein secondary structures. Several observations made in this task domain are rationalized in terms of the present model that, among others, provides a link between the seeming existence of an upper bound for the prediction efficiency and the amount of noise in the mapping.

Compiani, Mario; Fariselli, Piero; Casadio, Rita

1996-03-01

249

Experimental validation of finite element and boundary element methods for predicting structural vibration and radiated noise  

NASA Technical Reports Server (NTRS)

This research report is presented in three parts. In the first part, acoustical analyses were performed on modes of vibration of the housing of a transmission of a gear test rig developed by NASA. The modes of vibration of the transmission housing were measured using experimental modal analysis. The boundary element method (BEM) was used to calculate the sound pressure and sound intensity on the surface of the housing and the radiation efficiency of each mode. The radiation efficiency of each of the transmission housing modes was then compared to theoretical results for a finite baffled plate. In the second part, analytical and experimental validation of methods to predict structural vibration and radiated noise are presented. A rectangular box excited by a mechanical shaker was used as a vibrating structure. Combined finite element method (FEM) and boundary element method (BEM) models of the apparatus were used to predict the noise level radiated from the box. The FEM was used to predict the vibration, while the BEM was used to predict the sound intensity and total radiated sound power using surface vibration as the input data. Vibration predicted by the FEM model was validated by experimental modal analysis; noise predicted by the BEM was validated by measurements of sound intensity. Three types of results are presented for the total radiated sound power: sound power predicted by the BEM model using vibration data measured on the surface of the box; sound power predicted by the FEM/BEM model; and sound power measured by an acoustic intensity scan. In the third part, the structure used in part two was modified. A rib was attached to the top plate of the structure. The FEM and BEM were then used to predict structural vibration and radiated noise respectively. The predicted vibration and radiated noise were then validated through experimentation.

Seybert, A. F.; Wu, T. W.; Wu, X. F.

1994-01-01

250

TFaNS Tone Fan Noise Design/Prediction System. Volume 3; Evaluation of System Codes  

NASA Technical Reports Server (NTRS)

TFANS is the Tone Fan Noise Design/Prediction System developed by Pratt & Whitney under contract to NASA Lewis (presently NASA Glenn). The purpose of this system is to predict tone noise emanating from a fan stage including the effects of reflection and transmission by the rotor and stator and by the duct inlet and nozzle. These effects have been added to an existing annular duct/isolated stator noise prediction capability. TFANS consists of: The codes that compute the acoustic properties (reflection and transmission coefficients) of the various elements and write them to files. Cup3D: Fan Noise Coupling Code that reads these files, solves the coupling problem, and outputs the desired noise predictions. AWAKEN: CFD/Measured Wake Postprocessor which reformats CFD wake predictions and/or measured wake data so it can be used by the system. This volume of the report evaluates TFANS versus full-scale and ADP 22" fig data using the semi-empirical wake modelling in the system. This report is divided into three volumes: Volume 1: System Description, CUP3D Technical Documentation, and Manual for Code Developers; Volume II: User's Manual, TFANS Version 1.4; Volume III: Evaluation of System Codes.

Topol, David A.

1999-01-01

251

An instantaneous spatiotemporal model to predict a bicyclist's Black Carbon exposure based on mobile noise measurements  

NASA Astrophysics Data System (ADS)

Several studies have shown that a significant amount of daily air pollution exposure, in particular Black Carbon (BC), is inhaled during trips. Assessing this contribution to exposure remains difficult because on the one hand local air pollution maps lack spatio-temporal resolution, at the other hand direct measurement of particulate matter concentration remains expensive. This paper proposes to use in-traffic noise measurements in combination with geographical and meteorological information for predicting BC exposure during commuting trips. Mobile noise measurements are cheaper and easier to perform than mobile air pollution measurements and can easily be used in participatory sensing campaigns. The uniqueness of the proposed model lies in the choice of noise indicators that goes beyond the traditional overall A-weighted noise level used in previous work. Noise and BC exposures are both related to the traffic intensity but also to traffic speed and traffic dynamics. Inspired by theoretical knowledge on the emission of noise and BC, the low frequency engine related noise and the difference between high frequency and low frequency noise that indicates the traffic speed, are introduced in the model. In addition, it is shown that splitting BC in a local and a background component significantly improves the model. The coefficients of the proposed model are extracted from 200 commuter bicycle trips. The predicted average exposure over a single trip correlates with measurements with a Pearson coefficient of 0.78 using only four parameters: the low frequency noise level, wind speed, the difference between high and low frequency noise and a street canyon index expressing local air pollution dispersion properties.

Dekoninck, Luc; Botteldooren, Dick; Int Panis, Luc

2013-11-01

252

A Neuro-fuzzy Approach for Predicting the Effects of Noise Pollution on Human Work Efficiency  

Microsoft Academic Search

\\u000a In this paper, an attempt has been made to develop a neuro-fuzzy model for predicting the effects of noise pollution on human\\u000a work efficiency as a function of noise level, type of task, and exposure time. Originally, the model was developed using fuzzy\\u000a logic based on literature survey. So, the data used in the present study has been synthetically generated

Zaheeruddin; Garima

2004-01-01

253

Thermoelastic-damping noise from sapphire mirrors in a fundamental-noise-limited interferometer  

E-print Network

We report the first high-precision interferometer using large sapphire mirrors, and we present the first direct, broadband measurements of the fundamental thermal noise in these mirrors. Our results agree well with the thermoelastic-damping noise predictions of Braginsky, et al. [Phys. Lett. A 264, 1(1999)] and Cerdonio, et al.[Phys. Rev. D 63, 082003 (2001)], which have been used to predict the astrophysical reach of advanced interferometric gravitational wave detectors.

Eric D. Black; Akira Villar; Kenneth G. Libbrecht

2004-10-06

254

JT150 1/2-scale nozzle jet noise experiment and comparison with prediction  

NASA Technical Reports Server (NTRS)

As part of a program to study flight effects on the exhaust noise of a full scale JT15D engine, static half scale model jet noise experiments were conducted. Acoustic data were recorded for microphone angles of 45 deg to 155 deg with jet conditions for the model scale nozzle corresponding closely to those at 55, 73 and 97 percent of corrected rated speed for the full scale engine. These data are useful for determining the relative importance of jet and core noise in the static full scale engine test data and will in turn allow for a proper evaluation of flight effects on the exhaust noise results. The model scale data are also compared with the coaxial jet noise prediction. Above 1000 Hz, the prediction is nominally 0 to 3 dB higher than the data. The arithmetic mean of the differences between the experimental OASPL and the predicted OASPL for all angles for each run ranged from 0 to -3.2 dB. The standard deviation of all the OASPL differences is 2.2 dB. The discrepancies are greatest at low primary jet velocities and appear to be due to inadequacy in the variable jet density exponent incorporated in the prediction procedure.

Groesbeck, D. E.; Wasserbauer, C. A.

1983-01-01

255

ANOPP programmer's reference manual for the executive System. [aircraft noise prediction program  

NASA Technical Reports Server (NTRS)

Documentation for the Aircraft Noise Prediction Program as of release level 01/00/00 is presented in a manual designed for programmers having a need for understanding the internal design and logical concepts of the executive system software. Emphasis is placed on providing sufficient information to modify the system for enhancements or error correction. The ANOPP executive system includes software related to operating system interface, executive control, and data base management for the Aircraft Noise Prediction Program. It is written in Fortran IV for use on CDC Cyber series of computers.

Gillian, R. E.; Brown, C. G.; Bartlett, R. W.; Baucom, P. H.

1977-01-01

256

ASTRYD: A new numerical tool for aircraft cabin and environmental noise prediction  

NASA Astrophysics Data System (ADS)

ASTRYD is an analytical tool, developed originally for underwater applications, that computes acoustic pressure distribution around three-dimensional bodies in closed spaces like aircraft cabins. The program accepts data from measurements or other simulations, processes them in the time domain, and delivers temporal evolutions of the acoustic pressures and accelerations, as well as the radiated/diffracted pressure at arbitrary points located in the external/internal space. A typical aerospace application is prediction of acoustic load on satellites during the launching phase. An aeronautic application is engine noise distribution on a business jet body for prediction of environmental and cabin noise.

Berhault, J.-P.; Venet, G.; Clerc, C.

257

Noise Certification Predictions for FJX-2-Powered Aircraft Using Analytic Methods  

NASA Technical Reports Server (NTRS)

Williams International Co. is currently developing the 700-pound thrust class FJX-2 turbofan engine for the general Aviation Propulsion Program's Turbine Engine Element. As part of the 1996 NASA-Williams cooperative working agreement, NASA agreed to analytically calculate the noise certification levels of the FJX-2-powered V-Jet II test bed aircraft. Although the V-Jet II is a demonstration aircraft that is unlikely to be produced and certified, the noise results presented here may be considered to be representative of the noise levels of small, general aviation jet aircraft that the FJX-2 would power. A single engine variant of the V-Jet II, the V-Jet I concept airplane, is also considered. Reported in this paper are the analytically predicted FJX-2/V-Jet noise levels appropriate for Federal Aviation Regulation certification. Also reported are FJX-2/V-Jet noise levels using noise metrics appropriate for the propeller-driven aircraft that will be its major market competition, as well as a sensitivity analysis of the certification noise levels to major system uncertainties.

Berton, Jeffrey J.

1999-01-01

258

Effective Jet Properties for the Prediction of Turbulent Mixing Noise Reduction by Water Injection  

NASA Technical Reports Server (NTRS)

A one-dimensional control volume formulation is developed for the determination of jet mixing noise reduction due to water injection. The analysis starts from the conservation of mass, momentum and energy for the control volume, and introduces the concept of effective jet parameters (jet temperature, jet velocity and jet Mach number). It is shown that the water to jet mass flow rate ratio is an important parameter characterizing the jet noise reduction on account of gas-to-droplet momentum and heat transfer. Two independent dimensionless invariant groups are postulated, and provide the necessary relations for the droplet size and droplet Reynolds number. Results are presented illustrating the effect of mass flow rate ratio on the jet mixing noise reduction for a range of jet Mach number and jet Reynolds number. Predictions from the model show satisfactory comparison with available test data on supersonic jets. The results suggest that significant noise reductions can be achieved at increased flow rate ratios.

Kandula, Max; Lonergan, Michael J.

2007-01-01

259

The Prediction and Analysis of Jet Flows and Scattered Turbulent Mixing Noise About Flight Vehicle Airframes  

NASA Technical Reports Server (NTRS)

Jet flows interacting with nearby surfaces exhibit a complex behavior in which acoustic and aerodynamic characteristics are altered. The physical understanding and prediction of these characteristics are essential to designing future low noise aircraft. A new approach is created for predicting scattered jet mixing noise that utilizes an acoustic analogy and steady Reynolds-averaged Navier-Stokes solutions. A tailored Green's function accounts for the propagation of mixing noise about the air-frame and is calculated numerically using a newly developed ray tracing method. The steady aerodynamic statistics, associated unsteady sound source, and acoustic intensity are examined as jet conditions are varied about a large at plate. A non-dimensional number is proposed to estimate the effect of the aerodynamic noise source relative to jet operating condition and airframe position. The steady Reynolds-averaged Navier-Stokes solutions, acoustic analogy, tailored Green's function, non- dimensional number, and predicted noise are validated with a wide variety of measurements. The combination of the developed theory, ray tracing method, and careful implementation in a stand-alone computer program result in an approach that is more first principles oriented than alternatives, computationally efficient, and captures the relevant physics of fluid-structure interaction.

Miller, Steven A.

2014-01-01

260

The Prediction and Analysis of Jet Flows and Scattered Turbulent Mixing Noise about Flight Vehicle Airframes  

NASA Technical Reports Server (NTRS)

Jet flows interacting with nearby surfaces exhibit a complex behavior in which acoustic and aerodynamic characteristics are altered. The physical understanding and prediction of these characteristics are essential to designing future low noise aircraft. A new approach is created for predicting scattered jet mixing noise that utilizes an acoustic analogy and steady Reynolds-averaged Navier-Stokes solutions. A tailored Green's function accounts for the propagation of mixing noise about the airframe and is calculated numerically using a newly developed ray tracing method. The steady aerodynamic statistics, associated unsteady sound source, and acoustic intensity are examined as jet conditions are varied about a large flat plate. A non-dimensional number is proposed to estimate the effect of the aerodynamic noise source relative to jet operating condition and airframe position.The steady Reynolds-averaged Navier-Stokes solutions, acoustic analogy, tailored Green's function, non-dimensional number, and predicted noise are validated with a wide variety of measurements. The combination of the developed theory, ray tracing method, and careful implementation in a stand-alone computer program result in an approach that is more first principles oriented than alternatives, computationally efficient, and captures the relevant physics of fluid-structure interaction.

Miller, Steven A. E.

2014-01-01

261

A methodology for predicting impact-induced acoustic noise in machine systems  

NASA Astrophysics Data System (ADS)

A methodology for predicting noise and vibration of machines and their support structures is presented. Included is a heuristic energy-based criterion to assess the importance of dynamic coupling between a mechanism and its support structure based on a simplified analysis of a mechanism operating on a rigid base, which neglects the coupling. Also included is an analysis method that considers the coupling and to be used when the criterion reveals important coupling. The methodology is implemented using highly idealized closed form and more elaborate numerical descriptions and is checked against vibration and sound measurements of a plate subjected to periodic impacts by balls and a beam that rattles within a clearance bearing. The energy-based criterion is found to indicate situations in which mechanism-support coupling affects noise radiation. In some cases the coupling is observed to significantly affect vibration and noise radiation of the support structure, while having a relatively minor effect on mechanism response. Both the simple closed form and numerical descriptions are found to predict noise trends due to variations in machine speed and bearing clearance, and the numerical descriptions more accurately predict overall and band levels of noise radiation.

Oppenheimer, C. H.; Dubowsky, S.

2003-10-01

262

An outdoor noise propagation study to predict the effect of a power plant expansion  

NASA Astrophysics Data System (ADS)

The results of an outdoor noise propagation model using CadnaA were compared to test data obtained on-site. The subject property is the central utility plant of a hospital located in Milwaukee, scheduled to be expanded with the addition of cooling towers. The modeled area was 400 m squared with a resolution grid of 2 m squared. The model was used to validate the observed test data as well as to predict the anticipated noise levels at completion of the expansion. A total of 11 points were investigated and the predicted data were found to match the test values within 2 dB at many locations. The data from the model show that the anticipated noise levels at the East property line will exceed those mandated by local ordinances by 3 dB. The model also predicts that the addition of a three meter absorbing barrier and the use of reduced noise fans for the six cell cooling system will bring the overall noise level from the system into compliance.

Brasovan, Philip J.; Carney, Melinda J.; Cheenne, Dominique J.

2005-04-01

263

Computational methods in the prediction of advanced subsonic and supersonic propeller induced noise: ASSPIN users' manual  

NASA Technical Reports Server (NTRS)

This document describes the computational aspects of propeller noise prediction in the time domain and the use of high speed propeller noise prediction program ASSPIN (Advanced Subsonic and Supersonic Propeller Induced Noise). These formulations are valid in both the near and far fields. Two formulations are utilized by ASSPIN: (1) one is used for subsonic portions of the propeller blade; and (2) the second is used for transonic and supersonic regions on the blade. Switching between the two formulations is done automatically. ASSPIN incorporates advanced blade geometry and surface pressure modelling, adaptive observer time grid strategies, and contains enhanced numerical algorithms that result in reduced computational time. In addition, the ability to treat the nonaxial inflow case has been included.

Dunn, M. H.; Tarkenton, G. M.

1992-01-01

264

The prediction of jet noise ground effects using an acoustic analogy and a tailored Green's function  

NASA Astrophysics Data System (ADS)

An assessment of an acoustic analogy for the mixing noise component of jet noise in the presence of an infinite surface is presented. The reflection of jet noise by the ground changes the distribution of acoustic energy and is characterized by constructive and destructive interference patterns. The equivalent sources are modeled based on the two-point cross-correlation of the turbulent velocity fluctuations and a steady Reynolds-Averaged Navier-Stokes (RANS) solution. Propagation effects, due to reflection by the surface and refraction by the jet shear layer, are taken into account by calculating the vector Green's function of the linearized Euler equations (LEE). The vector Green's function of the LEE is written in relation to that of Lilley's equation; that is, it is approximated with matched asymptotic solutions and Green's function of the convective Helmholtz equation. The Green's function of the convective Helmholtz equation in the presence of an infinite flat plane with impedance is the Weyl-van der Pol equation. Predictions are compared with measurements from an unheated Mach 0.95 jet. Microphones are placed at various heights and distances from the nozzle exit in the peak jet noise direction above an acoustically hard and an asphalt surface. The predictions are shown to accurately capture jet noise ground effects that are characterized by constructive and destructive interference patterns in the mid- and far-field and capture overall trends in the near-field.

Miller, Steven A. E.

2014-02-01

265

The Prediction of Jet Noise Ground Effects Using an Acoustic Analogy and a Tailored Green's Function  

NASA Technical Reports Server (NTRS)

An assessment of an acoustic analogy for the mixing noise component of jet noise in the presence of an infinite surface is presented. The reflection of jet noise by the ground changes the distribution of acoustic energy and is characterized by constructive and destructive interference patterns. The equivalent sources are modeled based on the two-point cross- correlation of the turbulent velocity fluctuations and a steady Reynolds-Averaged Navier-Stokes (RANS) solution. Propagation effects, due to reflection by the surface and refaction by the jet shear layer, are taken into account by calculating the vector Green's function of the linearized Euler equations (LEE). The vector Green's function of the LEE is written in relation to Lilley's equation; that is, approximated with matched asymptotic solutions and the Green's function of the convective Helmholtz equation. The Green's function of the convective Helmholtz equation for an infinite flat plane with impedance is the Weyl-van der Pol equation. Predictions are compared with an unheated Mach 0.95 jet produced by a nozzle with an exit diameter of 0.3302 meters. Microphones are placed at various heights and distances from the nozzle exit in the peak jet noise direction above an acoustically hard and an asphalt surface. The predictions are shown to accurately capture jet noise ground effects that are characterized by constructive and destructive interference patterns in the mid- and far-field and capture overall trends in the near-field.

Miller, Steven A. E.

2013-01-01

266

Rotorcraft noise  

NASA Technical Reports Server (NTRS)

The establishment of a realistic plan for NASA and the U.S. helicopter industry to develop a design-for-noise methodology, including plans for the identification and development of promising noise reduction technology was discussed. Topics included: noise reduction techniques, scaling laws, empirical noise prediction, psychoacoustics, and methods of developing and validing noise prediction methods.

Huston, R. J. (compiler)

1982-01-01

267

Aircraft noise synthesis system  

NASA Technical Reports Server (NTRS)

A second-generation Aircraft Noise Synthesis System has been developed to provide test stimuli for studies of community annoyance to aircraft flyover noise. The computer-based system generates realistic, time-varying, audio simulations of aircraft flyover noise at a specified observer location on the ground. The synthesis takes into account the time-varying aircraft position relative to the observer; specified reference spectra consisting of broadband, narrowband, and pure-tone components; directivity patterns; Doppler shift; atmospheric effects; and ground effects. These parameters can be specified and controlled in such a way as to generate stimuli in which certain noise characteristics, such as duration or tonal content, are independently varied, while the remaining characteristics, such as broadband content, are held constant. The system can also generate simulations of the predicted noise characteristics of future aircraft. A description of the synthesis system and a discussion of the algorithms and methods used to generate the simulations are provided. An appendix describing the input data and providing user instructions is also included.

Mccurdy, David A.; Grandle, Robert E.

1987-01-01

268

Efficient Prediction of Helicopter BVI Noise under Different Conditions of Wake and Blade Deformation  

NASA Astrophysics Data System (ADS)

Predictions of helicopter BVI noise using three-dimensional Euler code with a single blade grid are conducted under three different conditions: BVI noise caused by (1) interaction between rotating blades and vortex shed from fixed wing vortex generator, (2) interaction between rotating blades and tip vortices shed from preceding blades, and (3) interaction between rotating blades with elastic deformation and shed tip vortices. In the CFD calculation, the Field Velocity Approach (FVA) and Scully’s vortex model are used to import the wake information into the calculation grid and to determine the induced velocity made by tip vortices, respectively (cases 1 3). Beddoes generalized wake model is used to prescribe the tip vortices position in the wake (cases 2 and 3). Information about blade elastic deformation is imported from HART II project experimental data into the calculation (case 3). Acoustic analyses based on Ffowcs-Williams and Hawkings (FW-H) equation are conducted subsequently in each case. The results from the calculations show good agreement with experiments in all three cases, indicating that application of FVA, Scully’s model, and Beddoes generalized wake model is effective for BVI noise prediction in this study, which is intended for low calculation cost using a single blade grid. Also, use of blade elastic deformation data in the calculation shows marked improvement in calculation precision. Consequently, the method used in this study can predict BVI noise under various conditions of wake or blade deformation with acceptable precision and low calculation cost.

Inada, Yoshinobu; Yang, Choongmo; Iwanaga, Noriki; Aoyama, Takashi

269

A review of propeller discrete frequency noise prediction technology with emphasis on two current methods for time domain calculations  

Microsoft Academic Search

A review of propeller noise prediction technology is presented which highlights the developments in the field from the successful attempt of Gutin to the current sophisticated techniques. Two methods for the prediction of the discrete frequency noise from conventional and advanced propellers in forward flight are described. These methods developed at MIT and NASA Langley Research Center are based on

F. Farassat; G. P. Succi

1980-01-01

270

Prediction of airplane aft-cabin noise using statistical energy analysis  

NASA Astrophysics Data System (ADS)

Statistical energy analysis (SEA) predictions of turbulent boundary layer and engine exhaust noise in the aft cabin of an airplane have been made and compared to flight data. Measurements of engine shock-cell sound pressure levels, characterized by relatively long correlation lengths and circumferential and axial variation along the fuselage surface, were extrapolated and used as source inputs to an SEA model of a widebody airplane fuselage. Turbulent boundary layer pressure fluctuations, characterized by relatively short circumferential correlation lengths and uniformity over the aft fuselage, were represented using Efimtsov empirical correlation functions. Model variance was predicted using the Langley method and combined with estimates of measurement uncertainty to verify the prediction process.

Fung, Andrew K.; Davis, Evan B.

2005-09-01

271

Prefiltering for improved unknown and known source correlation detection of broadband oscillatory transients and predicting the onset of paroxysmal atrial fibrillation using feature extraction and a hamming neural network  

NASA Astrophysics Data System (ADS)

The main focus of this study is to improve detection of deterministic broadband oscillatory transients in Gaussian noise using ordinary and higher order correlation detectors. Functional inputs to crosscorrelation, bicorrelation, and tricorrelation detectors are investigated assuming known, partially known, and unknown sources. Previous studies done by Pflug et al. (1999) showed that the correlation detection with functional inputs of broadband transients could not be improved as much as for narrowband transients or sinusoids. In this dissertation, a number of different functional inputs are studied, employing Monte Carlo simulations and generating signal-to-noise (SNR) detection curves. The most successful approach is bandpass filtering of the received signal input. Two suites of systematically generated broadband transients with varying center frequencies and signal widths are used to test this idea in detail. For the Gaussian modulated chirp and the partially known source assumption, the tricorrelation detector performed best in all cases. Improvement for the partially known source over the unknown source case is up to 12.5 dB for the best filter width. For the known source case, the optimal filter for the tricorrelation detector actually improves matched filter performance for the 50 Hz wide signal. Optimal filter width does not depend on center frequency for either source case. For the cosine tapered chirp and the partially known source assumption, improvements are up to 9.8 dB over the unknown source case. Here, the filtered autocorrelation input and tricorrelation detector perform best. However, the tricorrelation detector does not always outperform the crosscorrelation detector for the filtered signal input. In the case of the known source, the matched filter cannot be improved. The final chapter of this dissertation presents a different type of detection problem. The challenge is to develop an automated method that will detect the onset of paroxysmal atrial fibrillations (PAF) using Electrocardiograms (ECG) recorded immediately before an episode. Subjects that do not have PAF may be healthy or sick. The use of feature extraction combined with a Hamming neural network is proposed as a possible solution. Results are very encouraging with an average of 88% correct predictions among training and testing data.

Dean, Marcella Elsener

272

The 136 MHZ/400 MHz earth station antenna-noise temperature prediction program for RAE-B  

NASA Technical Reports Server (NTRS)

A simulation study was undertaken to determine the 136 MHz and 400 MHz noise temperature of the ground network antennas which will track the RAE-B satellite during data transmission periods. Since the noise temperature of the antenna effectively sets the signal-to-noise ratio of the received signal, a knowledge of SNR will be helpful in locating the optimum time windows for data transmission during low noise periods. Antenna noise temperatures will be predicted for selected earth-based ground stations which will support RAE-B. Telemetry data acquisition will be at 400 MHz; tracking support at 136 MHz will be provided by the Goddard Range and Range Rate (RARR) stations. The antenna-noise temperature predictions will include the effects of galactic-brightness temperature, the sun, and the brightest radio stars. Predictions will cover the ten-month period from March 1, 1973 to December 31, 1973.

Taylor, R. E.; Fee, J. J.; Chin, M.

1972-01-01

273

A computer program to predict rotor rotational noise of a stationary rotor from blade loading coefficient  

NASA Technical Reports Server (NTRS)

The programing language used is FORTRAN IV. A description of all main and subprograms is provided so that any user possessing a FORTRAN compiler and random access capability can adapt the program to his facility. Rotor blade surface-pressure spectra can be used by the program to calculate: (1) blade station loading spectra, (2) chordwise and/or spanwise integrated blade-loading spectra, and (3) far-field rotational noise spectra. Any of five standard inline functions describing the chordwise distribution of the blade loading can be chosen in order to study parametrically the acoustic predictions. The program output consists of both printed and graphic descriptions of the blade-loading coefficient spectra and far-field acoustic spectrum. The results may also be written on binary file for future processing. Examples of the application of the program along with a description of the rotational noise prediction theory on which the program is based are also provided.

Ramakrishnan, R.; Randall, D.; Hosier, R. N.

1976-01-01

274

Users' manual for the Langley high speed propeller noise prediction program (DFP-ATP)  

NASA Technical Reports Server (NTRS)

The use of the Dunn-Farassat-Padula Advanced Technology Propeller (DFP-ATP) noise prediction program which computes the periodic acoustic pressure signature and spectrum generated by propellers moving with supersonic helical tip speeds is described. The program has the capacity of predicting noise produced by a single-rotation propeller (SRP) or a counter-rotation propeller (CRP) system with steady or unsteady blade loading. The computational method is based on two theoretical formulations developed by Farassat. One formulation is appropriate for subsonic sources, and the other for transonic or supersonic sources. Detailed descriptions of user input, program output, and two test cases are presented, as well as brief discussions of the theoretical formulations and computational algorithms employed.

Dunn, M. H.; Tarkenton, G. M.

1989-01-01

275

An efficient and robust method for predicting helicopter rotor high-speed impulsive noise  

NASA Technical Reports Server (NTRS)

A new formulation for the Ffowcs Williams-Hawkings quadrupole source, which is valid for a far-field in-plane observer, is presented. The far-field approximation is new and unique in that no further approximation of the quadrupole source strength is made and integrands with r(exp -2) and r(exp -3) dependence are retained. This paper focuses on the development of a retarded-time formulation in which time derivatives are analytically taken inside the integrals to avoid unnecessary computational work when the observer moves with the rotor. The new quadrupole formulation is similar to Farassat's thickness and loading formulation 1A. Quadrupole noise prediction is carried out in two parts: a preprocessing stage in which the previously computed flow field is integrated in the direction normal to the rotor disk, and a noise computation stage in which quadrupole surface integrals are evaluated for a particular observer position. Preliminary predictions for hover and forward flight agree well with experimental data. The method is robust and requires computer resources comparable to thickness and loading noise prediction.

Brentner, Kenneth S.

1996-01-01

276

Measurement and prediction of noise from low-altitude military aircraft operations  

NASA Astrophysics Data System (ADS)

In response to the rapid growth in demand for information on noise levels around military airfields in the UK, NPL developed AIRNOISE, a mathematical model for computing aircraft noise contours. Since its first applications in 1981, the model has been used to determine zones of eligibility within the MoD compensation scheme. The model has been subject to continuous development, e.g., the incorporation of Harrier V/STOL operations. We have now extended the model to include noise from high-speed, low-level operations. The model predicts not only maximum levels but the complete time-history, so that the time-onset rate can be estimated. To aid refinement and validation of the model, a special exercise has been conducted in which Tornado, Harrier, Jaguar, Hawk, F-15 and F-16 aircraft have flown straight and level at heights between about 100 and 400 feet, at various speeds and engine power settings over an array of microphones. This paper describes the trial and the results obtained. The prediction model is outlined and comparisons made between predictions and measurements.

Barry, Bernard F.; Payne, Richard C.; Harris, Anthony L.; Weston, Ralph J.

1992-04-01

277

The Application of a Boundary Integral Equation Method to the Prediction of Ducted Fan Engine Noise  

NASA Technical Reports Server (NTRS)

The prediction of ducted fan engine noise using a boundary integral equation method (BIEM) is considered. Governing equations for the BIEM are based on linearized acoustics and describe the scattering of incident sound by a thin, finite-length cylindrical duct in the presence of a uniform axial inflow. A classical boundary value problem (BVP) is derived that includes an axisymmetric, locally reacting liner on the duct interior. Using potential theory, the BVP is recast as a system of hypersingular boundary integral equations with subsidiary conditions. We describe the integral equation derivation and solution procedure in detail. The development of the computationally efficient ducted fan noise prediction program TBIEM3D, which implements the BIEM, and its utility in conducting parametric noise reduction studies are discussed. Unlike prediction methods based on spinning mode eigenfunction expansions, the BIEM does not require the decomposition of the interior acoustic field into its radial and axial components which, for the liner case, avoids the solution of a difficult complex eigenvalue problem. Numerical spectral studies are presented to illustrate the nexus between the eigenfunction expansion representation and BIEM results. We demonstrate BIEM liner capability by examining radiation patterns for several cases of practical interest.

Dunn, M. H.; Tweed, J.; Farassat, F.

1999-01-01

278

Applications of the predictability of the Coherent Noise Model to aftershock sequences  

NASA Astrophysics Data System (ADS)

A study [1] of the coherent noise model [2-4] in natural time [5-7] has shown that it exhibits predictability. Interestingly, one of the predictors suggested [1] for the coherent noise model can be generalized and applied to the case of (real) aftershock sequences. The results obtained [8] so far are beyond chance. Here, we apply this approach to several aftershock sequences of strong earthquakes with magnitudes Mw ?6.9 in Indonesia, California and Greece, including the Mw9.2 earthquake that occurred on 26 December 2004 in Sumatra. References. [1] N. V. Sarlis and S.-R. G. Christopoulos, Predictability of the coherent-noise model and its applications, Physical Review E, 85, 051136, 2012. [2] M.E.J. Newman, Self-organized criticality, evolution and the fossil extinction record, Proc. R. Soc. London B, 263, 1605-1610, 1996. [3] M. E. J. Newman and K. Sneppen, Avalanches, scaling, and coherent noise, Phys. Rev. E, 54, 6226-6231, 1996. [4] K. Sneppen and M. Newman, Coherent noise, scale invariance and intermittency in large systems, Physica D, 110, 209 - 222. [5] P. Varotsos, N. Sarlis, and E. Skordas, Spatiotemporal complexity aspects on the interrelation between Seismic Electric Signals and seismicity, Practica of Athens Academy, 76, 294-321, 2001. [6] P.A. Varotsos, N.V. Sarlis, and E.S. Skordas, Long-range correlations in the electric signals that precede rupture, Phys. Rev. E, 66, 011902, 2002. [7] Varotsos P. A., Sarlis N. V. and Skordas E. S., Natural Time Analysis: The new view of time. Precursory Seismic Electric Signals, Earthquakes and other Complex Time-Series (Springer-Verlag, Berlin Heidelberg) 2011. [8] N. V. Sarlis and S.-R. G. Christopoulos, "Visualization of the significance of Receiver Operating Characteristics based on confidence ellipses", Computer Physics Communications, http://dx.doi.org/10.1016/j.cpc.2013.12.009

Christopoulos, Stavros-Richard; Sarlis, Nicholas

2014-05-01

279

A semi-analytical model for the prediction of underwater noise from offshore pile driving  

NASA Astrophysics Data System (ADS)

Underwater noise from offshore pile driving gained considerable attention in recent years mainly due to the large scale construction of offshore wind farms. The most common foundation type of a wind turbine is a monopile, upon which the wind tower rests. The pile is driven into place with the help of hydraulic hammers. During the hammering of the pile, high levels of noise are generated which are known to produce deleterious effects on both mammals and fish. In this work, a linear semi-analytical model is developed for predicting the levels of underwater noise for a wide range of system parameters. The model incorporates all major parts of the system. The hydraulic hammer is substituted by an external force, the pile is described as a thin circular cylindrical shell, the water is modelled as a compressible fluid and the water-saturated seabed is defined by distributed springs and dashpots in all directions. The solution of the coupled vibroacoustic problem is based on the representation of the response of the complete system on the modal basis of the in vacuo shell structure. The influence that the inter-modal coupling, the choice of the soil parameters and the acoustic impedance of the seabed have on the generated noise levels is studied in the frequency domain. Strong and weak points of the present model are discussed on the basis of a comparison with a set of available experimental data. The obtained results show the capability of the model to predict the underwater noise levels both qualitatively and quantitatively.

Tsouvalas, A.; Metrikine, A. V.

2013-06-01

280

The significance of parameter uncertainties for the prediction of offshore pile driving noise.  

PubMed

Due to the construction of offshore wind farms and its potential effect on marine wildlife, the numerical prediction of pile driving noise over long ranges has recently gained importance. In this contribution, a coupled finite element/wavenumber integration model for noise prediction is presented and validated by measurements. The ocean environment, especially the sea bottom, can only be characterized with limited accuracy in terms of input parameters for the numerical model at hand. Therefore the effect of these parameter uncertainties on the prediction of sound pressure levels (SPLs) in the water column is investigated by a probabilistic approach. In fact, a variation of the bottom material parameters by means of Monte-Carlo simulations shows significant effects on the predicted SPLs. A sensitivity analysis of the model with respect to the single quantities is performed, as well as a global variation. Based on the latter, the probability distribution of the SPLs at an exemplary receiver position is evaluated and compared to measurements. The aim of this procedure is to develop a model to reliably predict an interval for the SPLs, by quantifying the degree of uncertainty of the SPLs with the MC simulations. PMID:25373948

Lippert, Tristan; von Estorff, Otto

2014-11-01

281

Comparison of methods of predicting community response to impulsive and nonimpulsive noise  

NASA Technical Reports Server (NTRS)

Several scientific, regulatory, and policy-coordinating bodies have developed methods for predicting community response to sonic booms. The best known of these is the dosage-response relationship of Working Group 84 of the National Academy of Science's Committee on Hearing, Bioacoustics and Biomechanics. This dosage-response relationship between C-weighted DayNight Average Sound Level and the prevalence of annoyance with high energy impulsive sounds was derived from limited amounts of information about community response to regular, prolonged, and expected exposure to artillery and sonic booms. U.S. Army Regulation 201 adapts this approach to predictions of the acceptability of impulsive noise exposure in communities. This regulation infers equivalent degrees of effect with respect to a well known dosage-response relationship for general (nonimpulsive) transportation noise. Differences in prevalence of annoyance predicted by various relationships lead to different predictions of the compatibility of land uses with sonic boom exposure. An examination of these differences makes apparent several unresolved issues in current practice for predicting and interpreting the prevalence of annoyance due to sonic boom exposure.

Fidell, Sanford; Pearsons, Karl S.

1994-01-01

282

The Prediction of Noise Due to Jet Turbulence Convecting Past Flight Vehicle Trailing Edges  

NASA Technical Reports Server (NTRS)

High intensity acoustic radiation occurs when turbulence convects past airframe trailing edges. A mathematical model is developed to predict this acoustic radiation. The model is dependent on the local flow and turbulent statistics above the trailing edge of the flight vehicle airframe. These quantities are dependent on the jet and flight vehicle Mach numbers and jet temperature. A term in the model approximates the turbulent statistics of single-stream heated jet flows and is developed based upon measurement. The developed model is valid for a wide range of jet Mach numbers, jet temperature ratios, and flight vehicle Mach numbers. The model predicts traditional trailing edge noise if the jet is not interacting with the airframe. Predictions of mean-flow quantities and the cross-spectrum of static pressure near the airframe trailing edge are compared with measurement. Finally, predictions of acoustic intensity are compared with measurement and the model is shown to accurately capture the phenomenon.

Miller, Steven A. E.

2014-01-01

283

SNR Loss: A new objective measure for predicting speech intelligibility of noise-suppressed speech  

PubMed Central

Most of the existing intelligibility measures do not account for the distortions present in processed speech, such as those introduced by speech-enhancement algorithms. In the present study, we propose three new objective measures that can be used for prediction of intelligibility of processed (e.g., via an enhancement algorithm) speech in noisy conditions. All three measures use a critical-band spectral representation of the clean and noise-suppressed signals and are based on the measurement of the SNR loss incurred in each critical band after the corrupted signal goes through a speech enhancement algorithm. The proposed measures are flexible in that they can provide different weights to the two types of spectral distortions introduced by enhancement algorithms, namely spectral attenuation and spectral amplification distortions. The proposed measures were evaluated with intelligibility scores obtained by normal-hearing listeners in 72 noisy conditions involving noise-suppressed speech (consonants and sentences) corrupted by four different maskers (car, babble, train and street interferences). Highest correlation (r=?0.85) with sentence recognition scores was obtained using a variant of the SNR loss measure that only included vowel/consonant transitions and weak consonant information. High correlation was maintained for all noise types, with a maximum correlation (r=?0.88) achieved in street noise conditions. PMID:21503274

Ma, Jianfen; Loizou, Philipos C.

2010-01-01

284

Source Methodology for Turbofan Noise Prediction (SOURCE3D Technical Documentation)  

NASA Technical Reports Server (NTRS)

This report provides the analytical documentation for the SOURCE3D Rotor Wake/Stator Interaction Code. It derives the equations for the rotor scattering coefficients and stator source vector and scattering coefficients that are needed for use in the TFANS (Theoretical Fan Noise Design/Prediction System). SOURCE3D treats the rotor and stator as isolated source elements. TFANS uses this information, along with scattering coefficients for inlet and exit elements, and provides complete noise solutions for turbofan engines. SOURCE3D is composed of a collection of FORTRAN programs that have been obtained by extending the approach of the earlier V072 Rotor Wake/Stator Interaction Code. Similar to V072, it treats the rotor and stator as a collection of blades and vanes having zero thickness and camber contained in an infinite, hardwall annular duct. SOURCE3D adds important features to the V072 capability-a rotor element, swirl flow and vorticity waves, actuator disks for flow turning, and combined rotor/actuator disk and stator/actuator disk elements. These items allow reflections from the rotor, frequency scattering, and mode trapping, thus providing more complete noise predictions than previously. The code has been thoroughly verified through comparison with D.B. Hanson's CUP2D two- dimensional code using a narrow annulus test case.

Meyer, Harold D.

1999-01-01

285

Study of a low-dispersion finite volume scheme in rotorcraft noise prediction  

NASA Astrophysics Data System (ADS)

A Low-Dispersion Finite Volume (LDFV) scheme on curvilinear meshes has been applied to one-dimensional wave propagation simulation and rotorcraft noise prediction. This scheme minimizes dispersion error raised in modeling convection phenomena while keeping dissipation error small. It is accomplished by special high order polynomials that interpolate the properties at cell centers to the left and right sides of the cell surfaces. The fundamental one-dimensional wave propagation is simulated to give a direct comparison between the LDFV and existing MUSCL (Monotone Upstream-centered Scheme for Conservation Laws) schemes. Fourier analysis is employed to study numerical error generation and growth presented in the propagation of different frequency wave components with those schemes. The LDFV scheme has been implemented into a version of finite volume code TURNS (Transonic Unsteady Rotor Navier-Stokes) to simulate the High-Speed Impulsive (HSI) noise. A Superbee limiter is introduced to remove high frequency oscillations near the shock waves. Spherically symmetric wave propagation is modeled to investigate the behaviors of the MUSCL and LDFV schemes observed in the HSI noise prediction.

Wang, Gang

286

Prediction of scattering effects by sonic crystal noise barriers in 2d and 3d finite difference simulations  

E-print Network

Prediction of scattering effects by sonic crystal noise barriers in 2d and 3d finite difference 2012 Nantes Conference 23-27 April 2012, Nantes, France 995 #12;Sonic crystals have been investigated into something far more soothing [2]. The use of sonic crystals as a form of noise barrier has been the subject

Paris-Sud XI, Université de

287

METHODS AND TOOLS FOR MONITORING AND PREDICTION OF THE LARGE-SCALE ENVIRONMENTAL IMPACT OF RAILWAY NOISE  

Microsoft Academic Search

Due to environmental impact regulations there is a demand for methods and tools to determine noise reception levels near railway lines. Currently, a wide variety of methods and tools is available. Fast computers now enable us to develop powerful tools that combine simplified prediction methods with GIS systems. These new systems allow the study of noise reception levels and environmental

F. B. J. ELBERS

2000-01-01

288

Methods and Tools for Monitoring and Prediction of the Large-Scale Environmental Impact of Railway Noise  

Microsoft Academic Search

Due to environmental impact regulations there is a demand for methods and tools to determine noise reception levels near railway lines. Currently, a wide variety of methods and tools is available. Fast computers now enable us to develop powerful tools that combine simplified prediction methods with GIS systems. These new systems allow the study of noise reception levels and environmental

F. B. J. Elbers

2000-01-01

289

Quantification of advanced turboprop aircraft flyover noise annoyance  

NASA Technical Reports Server (NTRS)

A laboratory experiment was conducted to quantify the annoyance to advanced turboprop (propfan) aircraft flyover noise. A computer synthesis system was used to generate 45 realistic, time varying simulations of propeller aircraft flyover noise in which the tonal content was systematically varied to represent the factorial combinations of five fundamental frequencies, three frequency envelope shapes, and three tone-to-broadband noise ratios. In the experiment, 64 subjects judged the annoyance of recordings of the 45 synthesized flyover noises presented at three sound levels in a test facility which simulates the outdoor acoustic environment. Analyses of the judgements showed that frequency envelope shape did not significantly affect annoyance. The interaction of fundamental frequency with tone-to-broadband noise ratio did have a large and complex effect on annoyance. Duration corrected A-weighted sound pressure level with a modified tone correction predicted annoyance better than any other measurement procedure.

Mccurdy, D. A.

1984-01-01

290

Predicting the Inflow Distortion Tone Noise of the NASA Glenn Advanced Noise Control Fan with a Combined Quadrupole-Dipole Model  

NASA Technical Reports Server (NTRS)

A combined quadrupole-dipole model of fan inflow distortion tone noise has been extended to calculate tone sound power levels generated by obstructions arranged in circumferentially asymmetric locations upstream of a rotor. Trends in calculated sound power level agreed well with measurements from tests conducted in 2007 in the NASA Glenn Advanced Noise Control Fan. Calculated values of sound power levels radiated upstream were demonstrated to be sensitive to the accuracy of the modeled wakes from the cylindrical rods that were placed upstream of the fan to distort the inflow. Results indicate a continued need to obtain accurate aerodynamic predictions and measurements at the fan inlet plane as engineers work towards developing fan inflow distortion tone noise prediction tools.

Koch, L. Danielle

2012-01-01

291

Noise reduction using smart panel with shunt circuit  

Microsoft Academic Search

In this paper, piezoelectric smart panels featuring shunt damping are designed and tested for broadband noise reduction. Electrical admittance is introduced to represent electro-mechanical characteristics of piezoelectric smart structures and to predict the performance of piezoelectric shunt damping as a design index of the system. The location and size of piezoelectric patches on the host panel are optimized by taking

Li Jie Zhao; Heung Soo Kim; Jaehwan Kim

2006-01-01

292

Broadband radiometer  

DOEpatents

A broadband radiometer including (a) an optical integrating sphere having a enerally spherical integrating chamber and an entry port for receiving light (e.g., having visible and ultraviolet fractions), (b) a first optical radiation detector for receiving light from the sphere and producing an electrical output signal corresponding to broadband radiation, (c) a second optical radiation detector for receiving light from the sphere and producing an electrical output signal corresponding to a predetermined wavelength fraction of the broadband radiation, and (d) an output for producing an electrical signal which is proportional to the difference between the two electrical output signals. The radiometer is very useful, for example, in measuring the absolute amount of ultraviolet light present in a given light sample.

Cannon, Theodore W. (Golden, CO)

1994-01-01

293

Broadband radiometer  

DOEpatents

A broadband radiometer is disclosed including (a) an optical integrating sphere having generally spherical integrating chamber and an entry port for receiving light (e.g., having visible and ultraviolet fractions), (b) a first optical radiation detector for receiving light from the sphere and producing an electrical output signal corresponding to broadband radiation, (c) a second optical radiation detector for receiving light from the sphere and producing an electrical output signal corresponding to a predetermined wavelength fraction of the broadband radiation, and (d) an output for producing an electrical signal which is proportional to the difference between the two electrical output signals. The radiometer is very useful, for example, in measuring the absolute amount of ultraviolet light present in a given light sample. 8 figs.

Cannon, T.W.

1994-07-26

294

Analytical prediction of the interior noise for cylindrical models of aircraft fuselages for prescribed exterior noise fields. Phase 1: Development and validation of preliminary analytical models  

NASA Technical Reports Server (NTRS)

The basic theoretical work required to understand sound transmission into an enclosed space (that is, one closed by the transmitting structure) is developed for random pressure fields and for harmonic (tonal) excitation. The analysis is used to predict the noise reducton of unpressurized unstiffened cylinder, and also the interior response of the cylinder given a tonal (plane wave) excitation. Predictions and measurements are compared and the transmission is analyzed. In addition, results for tonal (harmonic) mechanical excitation are considered.

Pope, L. D.; Rennison, D. C.; Wilby, E. G.

1980-01-01

295

Hearing threshold and heart rate in men after repeated exposure to dynamic muscle work, sinusoidal vs stochastic whole body vibration and stable broadband noise  

Microsoft Academic Search

Changes in the temporary hearing threshold (TTS2) and heart rate (HR) were examined in subjects exposed to stable noise, whole body vibration and dynamic muscular work at a dry-bulb temperature of 30°C. The exposure combinations consisted of three categories of dynamic muscular work with varying loads (2 W, 4 W, 8 W), of two categories of noise and of three

Olavi Manninen

1984-01-01

296

On the prediction of impact noise, VII: The structural damping of machinery  

NASA Astrophysics Data System (ADS)

In earlier parts of this series of papers on the prediction of impact noise, it has been found that in predicting the noise energy radiated from an industrial machine, the only term in the energy accountancy equation which involves the true conversion of vibrational energy into heat is the quantity 10 log ?s; the other terms represent the fraction of impact energy entering the machine and the radiation efficiency change associated with moving this vibrational energy to lower frequencies. Thus the study of the overall damping factor ?s is of crucial importance to the accurate prediction of noise radiated. In spite of the large bibliography available on damping, the practical prediction of this quantity in industrial type machinery is so uncertain that many workers treat the quantity as an unknown "fudge factor" to be obtained from previous similar machines. This forbids the deliberate "designing in" of damping in a new machine, and leads to disappointment if new practices have inadvertently caused a significant loss in ?s, especially when, in fact, the previous versions were relatively highly damped. In this paper a study aimed at improving damping prediction is described. Based upon an investigation of the values of ?s obtained in industrial machinery structures, as opposed to "thin shell" viscoelastically damped structures, a review is presented of the levels of damping which can be obtained by various standard methods. The effects of bolts and fluid sloshing are included, and specific experiments are described on the effects of adding aggregates in cavities, adding close covers and fitting stick-slip springs on drill rods. There is ample evidence that adequate damping may be obtainable only by the additi·n of several of these palliatives to different parts of the machinery structure, and accordingly a possible method of summation is proposed, based upon an analogy with room acoustics. The study has led to a realization of the importance of obtaining a simple method of summating damping, and further work is now being done to validate such a method.

Richards, E. J.; Lenzi, A.

1984-12-01

297

Simplified combustion noise theory yielding a prediction of fluctuating pressure level  

NASA Technical Reports Server (NTRS)

The first order equations for the conservation of mass and momentum in differential form are combined for an ideal gas to yield a single second order partial differential equation in one dimension and time. Small perturbation analysis is applied. A Fourier transformation is performed that results in a second order, constant coefficient, nonhomogeneous equation. The driving function is taken to be the source of combustion noise. A simplified model describing the energy addition via the combustion process gives the required source information for substitution in the driving function. This enables the particular integral solution of the nonhomogeneous equation to be found. This solution multiplied by the acoustic pressure efficiency predicts the acoustic pressure spectrum measured in turbine engine combustors. The prediction was compared with the overall sound pressure levels measured in a CF6-50 turbofan engine combustor and found to be in excellent agreement.

Huff, R. G.

1984-01-01

298

Computation of interactional aerodynamics for noise prediction of heavy lift rotorcraft  

NASA Astrophysics Data System (ADS)

Many computational tools are used when developing a modern helicopter. As the design space is narrowed, more accurate and time-intensive tools are brought to bear. These tools are used to determine the effect of a design decision on the performance, handling, stability and efficiency of the aircraft. One notable parameter left out of this process is acoustics. This is due in part to the difficulty in making useful acoustics calculations that reveal the differences between various design configurations. This thesis presents a new approach designed to bridge the gap in prediction capability between fast but low-fidelity Lagrangian particle methods, and slow but high-fidelity Eulerian computational fluid dynamics simulations. A multi-pronged approach is presented. First, a simple flow solver using well-understood and tested flow solution methodologies is developed specifically to handle bodies in arbitrary motion. To this basic flow solver two new technologies are added. The first is an Immersed Boundary technique designed to be tolerant of geometric degeneracies and low-resolution grids. This new technique allows easy inclusion of complex fuselage geometries at minimal computational cost, improving the ability of a solver to capture the complex interactional aerodynamic effects expected in modern rotorcraft design. The second new technique is an extension of a concept from flow visualization where the motion of tip vortices are tracked through the solution using massless particles convecting with the local flow. In this extension of that concept, the particles maintain knowledge of the expected and actual vortex strength. As a post-processing step, when the acoustic calculations are made, these particles are used to augment the loading noise calculation and reproduce the highly-impulsive character of blade-vortex interaction noise. In combination these new techniques yield a significant improvement to the state of the art in rotorcraft blade-vortex interaction noise prediction.

Hennes, Christopher C.

299

Analysis of turbulent underexpanded jets. II - Shock noise features using SCIPVIS  

Microsoft Academic Search

SCIPVIS, the computational model discussed by Dash et al. (1985), is assessed in predicting the complicated flow structure associated with shock-containing plumes. In addition, the analysis in this study examines this code's applicability as a basic part of a program for estimating broadband shock noise radiation. The results of this study show that excellent agreement exists between predicted and measured

J. M. Seiner; S. M. Dash; D. E. Wolf

1985-01-01

300

Noise predictions for STM in systems with local electron nematic order Y. L. Loh,1,2 E. W. Carlson,2 and K. A. Dahmen3  

E-print Network

Noise predictions for STM in systems with local electron nematic order Y. L. Loh,1,2 E. W. Carlson received 11 May 2010; published 17 June 2010 We propose that thermal noise in local stripe orientation of the local I V curves. We predict the spatial, temporal, and thermal evolution of such noise, including

Carlson, Erica

301

Sources, control, and effects of noise from aircraft propellers and rotors  

NASA Astrophysics Data System (ADS)

Recent NASA and NASA sponsored research on the prediction and control of propeller and rotor source noise, on the analysis and design of fuselage sidewall noise control treatments, and on the measurement and quantification of the response of passengers to aircraft noise is described. Source noise predictions are compared with measurements for conventional low speed propellers, for new high speed propellers (propfans), and for a helicopter. Results from a light aircraft demonstration program are considered which indicates that about 5 dB reduction of flyover noise can be obtained without significant performance penalty. Sidewall design studies are examined for interior noise control in light general aviation aircraft and in large transports using propfan propulsion. The weight of the added acoustic treatment is estimated and tradeoffs between weight and noise reduction are discussed. A laboratory study of passenger response to combined broadband and tonal propeller-like noise is described. Subject discomfort ratings of combined tone broadband noises are compared with ratings of broadband (boundary layer) noise alone and the relative importance of the propeller tones is examined.

Mixson, J. S.; Greene, G. C.; Dempsey, T. K.

1981-04-01

302

Sources, control, and effects of noise from aircraft propellers and rotors  

NASA Technical Reports Server (NTRS)

Recent NASA and NASA sponsored research on the prediction and control of propeller and rotor source noise, on the analysis and design of fuselage sidewall noise control treatments, and on the measurement and quantification of the response of passengers to aircraft noise is described. Source noise predictions are compared with measurements for conventional low speed propellers, for new high speed propellers (propfans), and for a helicopter. Results from a light aircraft demonstration program are considered which indicates that about 5 dB reduction of flyover noise can be obtained without significant performance penalty. Sidewall design studies are examined for interior noise control in light general aviation aircraft and in large transports using propfan propulsion. The weight of the added acoustic treatment is estimated and tradeoffs between weight and noise reduction are discussed. A laboratory study of passenger response to combined broadband and tonal propeller-like noise is described. Subject discomfort ratings of combined tone broadband noises are compared with ratings of broadband (boundary layer) noise alone and the relative importance of the propeller tones is examined.

Mixson, J. S.; Greene, G. C.; Dempsey, T. K.

1981-01-01

303

Real-Scale Measurement Results for Audible Noise from AC Overhead Transmission Lines and Prediction Formula in Heavy Rain  

NASA Astrophysics Data System (ADS)

The audible noise produced by corona discharge from AC overhead transmission line conductors is one of the major factors affecting the design of conductors, particularly for transmission lines with voltages above 500 kV. The audible noise has two components, which are random noise with frequency components from several hundreds to 20 kHz and pure tones with a power line frequency and frequency components of its even multiples. In this paper, measurement results for random noise in heavy rain using a real-scale facility, namely, UHV corona cage, which has a cross section of 8 m×8 m and a length of 24 m, are shown and a new prediction formula for the sound level of random noise in heavy rain is proposed.

Tanabe, Kazuo

304

TFaNS Tone Fan Noise Design/Prediction System. Volume 2; User's Manual; 1.4  

NASA Technical Reports Server (NTRS)

TFaNS is the Tone Fan Noise Design/Prediction System developed by Pratt & Whitney under contract to NASA Lewis (presently NASA Glenn). The purpose of this system is to predict tone noise emanating from a fan stage including the effects of reflection and transmission by the rotor and stator and by the duct inlet and nozzle. These effects have been added to an existing annular duct/isolated stator noise prediction capability. TFaNS consists of: the codes that compute the acoustic properties (reflection and transmission coefficients) of the various elements and write them to files. CUP3D: Fan Noise Coupling Code that reads these files, solves the coupling problem, and outputs the desired noise predictions. AWAKEN: CFD/Measured Wake Postprocessor which reformats CFD wake predictions and/or measured wake data so it can be used by the system. This volume of the report provides information on code input and file structure essential for potential users of TFANS. This report is divided into three volumes: Volume 1. System Description, CUP3D Technical Documentation, and Manual for Code Developers; Volume 2. User's Manual, TFANS Vers. 1.4; Volume 3. Evaluation of System Codes.

Topol, David A.; Eversman, Walter

1999-01-01

305

Noise and randomlike behavior of perceptrons: Theory and applicationto protein structure prediction  

Microsoft Academic Search

In the first part of this paper we study the performance of a single-layer perceptron that is expected to classify patterns into classes in the case where the mapping to be learned is corrupted by noise. Extending previous results concerning the statistical behavior of perceptrons, we distinguish two mutually exclusive kinds of noise (I noise and R noise) and study

M. Compiani; P. Fariselli; R. Casadio

1997-01-01

306

Temporal Characterization of Aircraft Noise Sources  

NASA Technical Reports Server (NTRS)

Current aircraft source noise prediction tools yield time-independent frequency spectra as functions of directivity angle. Realistic evaluation and human assessment of aircraft fly-over noise require the temporal characteristics of the noise signature. The purpose of the current study is to analyze empirical data from broadband jet and tonal fan noise sources and to provide the temporal information required for prediction-based synthesis. Noise sources included a one-tenth-scale engine exhaust nozzle and a one-fifth scale scale turbofan engine. A methodology was developed to characterize the low frequency fluctuations employing the Short Time Fourier Transform in a MATLAB computing environment. It was shown that a trade-off is necessary between frequency and time resolution in the acoustic spectrogram. The procedure requires careful evaluation and selection of the data analysis parameters, including the data sampling frequency, Fourier Transform window size, associated time period and frequency resolution, and time period window overlap. Low frequency fluctuations were applied to the synthesis of broadband noise with the resulting records sounding virtually indistinguishable from the measured data in initial subjective evaluations. Amplitude fluctuations of blade passage frequency (BPF) harmonics were successfully characterized for conditions equivalent to take-off and approach. Data demonstrated that the fifth harmonic of the BPF varied more in frequency than the BPF itself and exhibited larger amplitude fluctuations over the duration of the time record. Frequency fluctuations were found to be not perceptible in the current characterization of tonal components.

Grosveld, Ferdinand W.; Sullivan, Brenda M.; Rizzi, Stephen A.

2004-01-01

307

Advanced turboprop aircraft flyover noise annoyance - Comparison of different propeller configurations  

NASA Technical Reports Server (NTRS)

A laboratory experiment was conducted to compare the annoyance of flyover noise from advanced turboprop aircraft having different propeller configurations with the annoyance of conventional turboprop and jet aircraft flyover noise. It was found that advanced turboprops with single-rotating propellers were, on average, slightly less annoying than the other aircraft. Fundamental frequency and tone-to-broadband noise ratio affected annoyance response to advanced turboprops but the effects varied with propeller configuration and noise metric. The addition of duration corrections and corrections for tones above 500 Hz to the noise measurement procedures improved prediction ability.

Mccurdy, David A.

1989-01-01

308

Noise characterization of broadband fiber Cherenkov radiation as a visible-wavelength source for optical coherence tomography and two-photon fluorescence microscopy.  

PubMed

Optical sources in the visible region immediately adjacent to the near-infrared biological optical window are preferred in imaging techniques such as spectroscopic optical coherence tomography of endogenous absorptive molecules and two-photon fluorescence microscopy of intrinsic fluorophores. However, existing sources based on fiber supercontinuum generation are known to have high relative intensity noise and low spectral coherence, which may degrade imaging performance. Here we compare the optical noise and pulse compressibility of three high-power fiber Cherenkov radiation sources developed recently, and evaluate their potential to replace the existing supercontinuum sources in these imaging techniques. PMID:25321223

Tu, Haohua; Zhao, Youbo; Liu, Yuan; Liu, Yuan-Zhi; Boppart, Stephen

2014-08-25

309

Combustion noise  

NASA Technical Reports Server (NTRS)

A review of the subject of combustion generated noise is presented. Combustion noise is an important noise source in industrial furnaces and process heaters, turbopropulsion and gas turbine systems, flaring operations, Diesel engines, and rocket engines. The state-of-the-art in combustion noise importance, understanding, prediction and scaling is presented for these systems. The fundamentals and available theories of combustion noise are given. Controversies in the field are discussed and recommendations for future research are made.

Strahle, W. C.

1977-01-01

310

Fuselage panel noise attenuation by piezoelectric switching control  

NASA Astrophysics Data System (ADS)

This paper describes a problem that we encountered in our noise attenuation project and our solution for it. We intend to attenuate low-frequency noise that transmits through aircraft fuselage panels. Our method of noise attenuation is implemented with a piezoelectric semi-active system having a selective switch instead of an active energy-supply system. The semi-active controller is based on the predicted sound pressure distribution obtained from acoustic emission analysis. Experiments and numerical simulations demonstrate that the semi-active method attenuates acoustic levels of not only the simple monochromatic noise but also of broadband noise. We reveal that tuning the electrical parameters in the circuit is the key to effective noise attenuation, to overcome the acoustic excitation problem due to sharp switching actions, as well as to control chattering problems. The results obtained from this investigation provide meaningful insights into designing noise attenuation systems for comfortable aircraft cabin environments.

Makihara, Kanjuro; Miyakawa, Takeya; Onoda, Junjiro; Minesugi, Kenji

2010-08-01

311

Validation of finite element computations for the quantitative prediction of underwater noise from impact pile driving.  

PubMed

The acoustic radiation from a pile being driven into the sediment by a sequence of hammer strikes is studied with a linear, axisymmetric, structural acoustic frequency domain finite element model. Each hammer strike results in an impulsive sound that is emitted from the pile and then propagated in the shallow water waveguide. Measurements from accelerometers mounted on the head of a test pile and from hydrophones deployed in the water are used to validate the model results. Transfer functions between the force input at the top of the anvil and field quantities, such as acceleration components in the structure or pressure in the fluid, are computed with the model. These transfer functions are validated using accelerometer or hydrophone measurements to infer the structural forcing. A modeled hammer forcing pulse is used in the successive step to produce quantitative predictions of sound exposure at the hydrophones. The comparison between the model and the measurements shows that, although several simplifying assumptions were made, useful predictions of noise levels based on linear structural acoustic models are possible. In the final part of the paper, the model is used to characterize the pile as an acoustic radiator by analyzing the flow of acoustic energy. PMID:23297884

Zampolli, Mario; Nijhof, Marten J J; de Jong, Christ A F; Ainslie, Michael A; Jansen, Erwin H W; Quesson, Benoit A J

2013-01-01

312

AN INVESTIGATION OF A THEORETICAL TOOL FOR PREDICTING PERFORMANCE OF AN ACTIVE NOISE  

E-print Network

loudspeakers with both sound reproduction and active noise control in mind. 1. Introduction Active noise relax the need for sound insulating materials, leading to lighter vehicles with lower fuel consumption. As modern cars typically contain several loudspeakers, their sound systems could be used also for noise

313

Tone Noise Predictions for a Spacecraft Cabin Ventilation Fan Ingesting Distorted Inflow and the Challenges of Validation  

NASA Technical Reports Server (NTRS)

A fan tone noise prediction code has been developed at NASA Glenn Research Center that is capable of estimating duct mode sound power levels for a fan ingesting distorted inflow. This code was used to predict the circumferential and radial mode sound power levels in the inlet and exhaust duct of an axial spacecraft cabin ventilation fan. Noise predictions at fan design rotational speed were generated. Three fan inflow conditions were studied: an undistorted inflow, a circumferentially symmetric inflow distortion pattern (cylindrical rods inserted radially into the flowpath at 15deg, 135deg, and 255deg), and a circumferentially asymmetric inflow distortion pattern (rods located at 15deg, 52deg and 173deg). Noise predictions indicate that tones are produced for the distorted inflow cases that are not present when the fan operates with an undistorted inflow. Experimental data are needed to validate these acoustic predictions, as well as the aerodynamic performance predictions. Given the aerodynamic design of the spacecraft cabin ventilation fan, a mechanical and electrical conceptual design study was conducted. Design features of a fan suitable for obtaining detailed acoustic and aerodynamic measurements needed to validate predictions are discussed.

Koch, L. Danielle; Shook, Tony D.; Astler, Douglas T.; Bittinger, Samantha A.

2011-01-01

314

Tone Noise Predictions for a Spacecraft Cabin Ventilation Fan Ingesting Distorted Inflow and the Challenges of Validation  

NASA Technical Reports Server (NTRS)

A fan tone noise prediction code has been developed at NASA Glenn Research Center that is capable of estimating duct mode sound power levels for a fan ingesting distorted inflow. This code was used to predict the circumferential and radial mode sound power levels in the inlet and exhaust duct of an axial spacecraft cabin ventilation fan. Noise predictions at fan design rotational speed were generated. Three fan inflow conditions were studied: an undistorted inflow, a circumferentially symmetric inflow distortion pattern (cylindrical rods inserted radially into the flowpath at 15deg, 135deg, and 255deg), and a circumferentially asymmetric inflow distortion pattern (rods located at 15deg, 52deg and 173deg). Noise predictions indicate that tones are produced for the distorted inflow cases that are not present when the fan operates with an undistorted inflow. Experimental data are needed to validate these acoustic predictions, as well as the aerodynamic performance predictions. Given the aerodynamic design of the spacecraft cabin ventilation fan, a mechanical and electrical conceptual design study was conducted. Design features of a fan suitable for obtaining detailed acoustic and aerodynamic measurements needed to validate predictions are discussed.

Koch, L. Danielle; Shook, Tony D.; Astler, Douglas T.; Bittinger, Samantha A.

2012-01-01

315

Broadband asymmetric acoustic transmission in a gradient-index structure  

NASA Astrophysics Data System (ADS)

We propose a scheme of realizing broadband asymmetric acoustic transmission using gradient-index structure, and demonstrate an implementation utilizing phononic-crystal-based metamaterials which can realize an idealized model with desired parameters. The asymmetric transmission is valid within a remarkably broad frequency range. This phenomenon stems from the break of the geometric symmetry of wave trajectories along two opposite directions, essentially different from the mechanisms of previous designs. The numerical results agree well with the analytical predictions using acoustic ray theory. Our design may have potential applications in many fields such as ultrasonic therapy and noise control.

Li, Rui-Qi; Liang, Bin; Li, Yong; Kan, Wei-Wei; Zou, Xin-Ye; Cheng, Jian-Chun

2012-12-01

316

A computer model to predict traffic noise in urban situations under free flow and traffic light conditions  

Microsoft Academic Search

A computer model is presented for predicting traffic noise indices in built-up situations for free flow traffic conditions and for a flow interrupted by a traffic light. The stream of vehicles is simulated by a given time headway distribution, and a transfer function obtained from a 1 : 100 scale model is used to simulate the specific built-up situation. Different

L. J. M. Jacobs; L. Nijs; J. J. van Willigenburg

1980-01-01

317

UNDERSTANDING THE INFLUENCE OF NOISE, SAMPLING DENSITY AND DATA DISTRIBUTION ON SPATIAL PREDICTION QUALITY THROUGH THE USE OF  

E-print Network

UNDERSTANDING THE INFLUENCE OF NOISE, SAMPLING DENSITY AND DATA DISTRIBUTION ON SPATIAL PREDICTION and Computer Science, Washington State University, Pullman WA 99164 USA E-mail: dpokraja@eecs.wsu.edu Zoran Obradovic School of Electrical Engineering and Computer Science, Washington State University, Pullman WA

Obradovic, Zoran

318

TFaNS-Tone Fan Noise Design/Prediction System: Users' Manual TFaNS Version 1.5  

NASA Technical Reports Server (NTRS)

TFaNS is the Tone Fan Noise Design/Prediction System developed by Pratt & Whitney under contract to NASA Glenn. The purpose of this system is to predict tone noise emanating from a fan stage including the effects of reflection and transmission by the rotor and stator and by the duct inlet and nozzle. The first version of this design system was developed under a previous NASA contract. Several improvements have been made to TFaNS. This users' manual shows how to run this new system. TFaNS consists of the codes that compute the acoustic properties (reflection and transmission coefficients) of the various elements and writes them to files, CUP3D Fan Noise Coupling Code that reads these files, solves the coupling problem, and outputs the desired noise predictions, and AWAKEN CFD/Measured Wake Postprocessor which reformats CFD wake predictions and/or measured wake data so they can be used by the system. This report provides information on code input and file structure essential for potential users of TFaNS.

Topol, David A.; Huff, Dennis L. (Technical Monitor)

2003-01-01

319

Applicability of characterized source model to prediction of broad-band strong ground motion for scenario earthquakes  

Microsoft Academic Search

Most of the uncertainties in predicting strong ground motion is to model source heterogeneities of future earthquakes. An available method we propose for characterizing the heterogeneous slip distribution on the fault plane is based on the empirical source characterization derived from the slip models of the crustal earthquakes by Somerville et al. (1999). Areas of asperities having large slips are

k kamae; k irikura

2001-01-01

320

Aeroacoustic Prediction Codes  

NASA Technical Reports Server (NTRS)

This report describes work performed on Contract NAS3-27720AoI 13 as part of the NASA Advanced Subsonic Transport (AST) Noise Reduction Technology effort. Computer codes were developed to provide quantitative prediction, design, and analysis capability for several aircraft engine noise sources. The objective was to provide improved, physics-based tools for exploration of noise-reduction concepts and understanding of experimental results. Methods and codes focused on fan broadband and 'buzz saw' noise and on low-emissions combustor noise and compliment work done by other contractors under the NASA AST program to develop methods and codes for fan harmonic tone noise and jet noise. The methods and codes developed and reported herein employ a wide range of approaches, from the strictly empirical to the completely computational, with some being semiempirical analytical, and/or analytical/computational. Emphasis was on capturing the essential physics while still considering method or code utility as a practical design and analysis tool for everyday engineering use. Codes and prediction models were developed for: (1) an improved empirical correlation model for fan rotor exit flow mean and turbulence properties, for use in predicting broadband noise generated by rotor exit flow turbulence interaction with downstream stator vanes: (2) fan broadband noise models for rotor and stator/turbulence interaction sources including 3D effects, noncompact-source effects. directivity modeling, and extensions to the rotor supersonic tip-speed regime; (3) fan multiple-pure-tone in-duct sound pressure prediction methodology based on computational fluid dynamics (CFD) analysis; and (4) low-emissions combustor prediction methodology and computer code based on CFD and actuator disk theory. In addition. the relative importance of dipole and quadrupole source mechanisms was studied using direct CFD source computation for a simple cascadeigust interaction problem, and an empirical combustor-noise correlation model was developed from engine acoustic test results. This work provided several insights on potential approaches to reducing aircraft engine noise. Code development is described in this report, and those insights are discussed.

Gliebe, P; Mani, R.; Shin, H.; Mitchell, B.; Ashford, G.; Salamah, S.; Connell, S.; Huff, Dennis (Technical Monitor)

2000-01-01

321

Helicopter noise as predicted by three-dimensional monopole and quasi-steady full-potential dipole sources  

NASA Technical Reports Server (NTRS)

A three-dimensional quasi-steady full-potential rotor-flow-analysis program, called ROT22 developed at NASA Ames Research Center is run in conjunction with Farassat's (1981) helicopter-noise-prediction code to assess the thickness and loading noises made by a rotor blade. As a model example, the case of a 1/7th UH-1H NACA-0012-profile straight nonlifting rotor blade in hover is studied. Results for tip Mach numbers ranging from .4 to .962 are presented. Also presented is the effect of blade-tip loading on the overall noise and of profile curvature on the thickness noise. The study confirms that the blade volume displacement is a dominant source of helicopter noise and further concludes that the blade tip makes only a small noise contribution that steadily decreases with increasing tip Mach numbers, and that the inclusion of blade profile curvature tends to improve the negative peak amplitudes overpredicted by Schmitz and Yu (1983).

Aggarwal, H. R.

1984-01-01

322

The prediction of the noise of supersonic propellers in time domain - New theoretical results  

NASA Technical Reports Server (NTRS)

In this paper, a new formula for the prediction of the noise of supersonic propellers is derived in the time domain which is superior to the previous formulations in several respects. The governing equation is based on the Ffowcs Williams-Hawkings (FW-H) equation with the thickness source term replaced by an equivalent loading source term derived by Isom (1975). Using some results of generalized function theory and simple four-dimensional space-time geometry, the formal solution of the governing equation is manipulated to a form requiring only the knowledge of blade surface pressure data and geometry. The final form of the main result of this paper consists of some surface and line integrals. The surface integrals depend on the surface pressure, time rate of change of surface pressure, and surface pressure gradient. These integrals also involve blade surface curvatures. The line integrals which depend on local surface pressure are along the trailing edge, the shock traces on the blade, and the perimeter of the airfoil section at the inner radius of the blade. The new formulation is for the full blade surface and does not involve any numerical observer time differentiation. The method of implementation on a computer for numerical work is also discussed.

Farassat, F.

1983-01-01

323

Prediction and evaluation of noise pollution caused by a roads network  

Microsoft Academic Search

?è ?è?è?è?è Abstract According to OECD, at least 20% of the European Union population (around 80 million of people) is exposed in daytime to traffic noise, whose level exceeds the limit of 65 dB(A); traffic represents today the main source of noise in most European countries. Italian laws are very concerned about noise pollution; in particular law no. 447\\/95 states

Francesco Asdrubali; Carlo Costantini

324

Computer-program model for predicting horizontally and vertically polarized VLF atmospheric radio noise at elevated receivers  

NASA Astrophysics Data System (ADS)

A computer program was developed that can predict horizontally and vertically polarized atmospheric radio noise at any altitude or location in the Earth-ionosphere waveguide in the very-low-frequency (VLF) range from 10 to 30 kHz. The new program, HORNS, uses the outputs of two previously written programs, COMPWR and NOISLAN, which predict the vertical electric noise field at the ground. The HORNS program computes all the field components at any altitude using the vertical electric field at the Earth's surface as a basis. Predicted values from several versions of the new model were compared with presently available data. The results are encouraging, but more data are needed to test the model.

Kelly, F. J.; Hauser, J. P.; Rhoads, F. J.

1981-12-01

325

Significance of shock structure on supersonic jet mixing noise of axisymmetric nozzles  

NASA Technical Reports Server (NTRS)

One of the key technical elements in NASA's high speed research program is reducing the noise level to meet the federal noise regulation. The dominant noise source is associated with the supersonic jet discharged from the engine exhaust system. Whereas the turbulence mixing is largely responsible for the generation of the jet noise, a broadband shock-associated noise is also generated when the nozzle operates at conditions other than its design. For both mixing and shock noise components, because the source of the noise is embedded in the jet plume, one can expect that jet noise can be predicted from the jet flowfield computation. Mani et al. developed a unified aerodynamic/acoustic prediction scheme by applying an extension of Reichardt's aerodynamic model to compute turbulent shear stresses which are utilized in estimating the strength of the noise source. Although this method produces a fast and practical estimate of the jet noise, a modification by Khavaran et al. has led to an improvement in aerodynamic solution. The most notable feature in this work is that Reichardt's model is replaced with the computational fluid dynamics (CFD) solution of Reynolds-averaged Navier-Stokes equations. The major advantage of this work is that the essential, noise-related flow quantities such as turbulence intensity and shock strength can be better predicted. The predictions were limited to a shock-free design condition and the effect of shock structure on the jet mixing noise was not addressed. The present work is aimed at investigating this issue. Under imperfectly expanded conditions the existence of the shock cell structure and its interaction with the convecting turbulence structure may not only generate a broadband shock-associated noise but also change the turbulence structure, and thus the strength of the mixing noise source. Failure in capturing shock structures properly could lead to incorrect aeroacoustic predictions.

Kim, Chan M.; Krejsa, Eugene A.; Khavaran, Abbas

1994-01-01

326

Analysis and Synthesis of Tonal Aircraft Noise Sources  

NASA Technical Reports Server (NTRS)

Fixed and rotary wing aircraft operations can have a significant impact on communities in proximity to airports. Simulation of predicted aircraft flyover noise, paired with listening tests, is useful to noise reduction efforts since it allows direct annoyance evaluation of aircraft or operations currently in the design phase. This paper describes efforts to improve the realism of synthesized source noise by including short term fluctuations, specifically for inlet-radiated tones resulting from the fan stage of turbomachinery. It details analysis performed on an existing set of recorded turbofan data to isolate inlet-radiated tonal fan noise, then extract and model short term tonal fluctuations using the analytic signal. Methodologies for synthesizing time-variant tonal and broadband turbofan noise sources using measured fluctuations are also described. Finally, subjective listening test results are discussed which indicate that time-variant synthesized source noise is perceived to be very similar to recordings.

Allen, Matthew P.; Rizzi, Stephen A.; Burdisso, Ricardo; Okcu, Selen

2012-01-01

327

Evaluation and prediction of noise pollution levels in urban areas of Cdiz (Spain)  

Microsoft Academic Search

In the European policy, one of the most important objectives is to achieve a high level of health and environmental protection. The latest studies have shown that more than 20% of the world population lives under unacceptable noise levels and near 60% of the European population is exposed to worrying noise levels during the day. So, nowadays one of the

Silvia Rivas; Ricardo Hernandez; Jose Luis Cueto

2003-01-01

328

PREDICTION OF SUPERSONIC JET NOISE FROM A STATISTICAL ACOUSTIC MODEL AND A COMPRESSIBLE TURBULENCE CLOSURE  

Microsoft Academic Search

Acoustic radiation of shock free supersonic jets is modified in comparison with subsonic jet noise because of Mach wave emission. Intense noise is radiated when turbulent structures are convected supersonically relative to the ambient sound speed. Using the framework of Lighthill's equation, Ffowcs Williams and Maidanik developed an approximation of Lighthill's term for a supersonically converted acoustic source in a

C. Bailly; S. Candel; P. Lafon

1996-01-01

329

5th International Meeting Wind Turbine Noise  

E-print Network

1 5th International Meeting on Wind Turbine Noise Denver 28 ­ 30 August 2013 Wind Turbine Noise Broadband noise generated aerodynamically is the dominant noise source for a modern wind turbine(Brooks et, clean energy. While profiting from wind energy, the noise produced by a modern wind turbine becomes

Paris-Sud XI, Université de

330

A three-dimensional vibroacoustic model for the prediction of underwater noise from offshore pile driving  

NASA Astrophysics Data System (ADS)

Steel monopiles are nowadays widely used as foundations for a large number of offshore structures. The installation procedure commonly involves a pile driving process which can last up to several hours depending upon pile dimensions, soil conditions and input energy of the hydraulic hammer. In impact pile driving, a hydraulic hammer delivers a series of hammer blows at the head of the pile that drive the pile into the sediment. Each hammer strike results in pile vibrations that emit strong impulsive sounds into the water column which can be harmful for the marine ecosystem. With today's increasing concern regarding the environmental impact of such operations, engineering tools which will be able to provide reliable predictions of the underwater noise levels are required. In this study, a linear semi-analytical formulation of the coupled vibroacoustics of a complete pile-water-soil interaction model is addressed. The pile is described by a high order thin shell theory whereas both water and soil are modelled as three-dimensional continua. Results obtained with the developed model indicate that the near-field response in the water column consists mainly of pressure conical waves generated by the supersonic compressional waves in the pile excited by the impact hammer. The soil response is dominated by shear waves with almost vertical polarization. The Scholte waves are also generated at the water-seabed interface which can produce pressure fluctuations in the water column that are particularly significant close to the sea floor. The effects of soil elasticity and pile size are thoroughly investigated and their influence on the generated pressure levels is highlighted. The results are also compared with those ones of a similar model in which the soil is treated as an equivalent acoustic fluid. It is shown that the latter approximation can yield inaccurate results at low frequencies especially for harder soil sediments.

Tsouvalas, A.; Metrikine, A. V.

2014-04-01

331

Theoretical predictions for the effect of nebular emission on the broad-band photometry of high-redshift galaxies  

NASA Astrophysics Data System (ADS)

By combining optical and near-IR observations from the Hubble Space Telescope with near-IR photometry from the Spitzer Space Telescope, it is possible to measure the rest-frame UV-optical colours of galaxies at z = 4-8. The UV-optical spectral energy distribution of star formation dominated galaxies is the result of several different factors. These include the joint distribution of stellar masses, ages and metallicities (solely responsible for the pure stellar spectral energy distribution), and the subsequent reprocessing by dust and gas in the interstellar medium. Using a large cosmological hydrodynamical simulation (MassiveBlack-II), we investigate the predicted spectral energy distributions of galaxies at high redshift with a particular emphasis on assessing the potential contribution of nebular emission. We find that the average (median) pure stellar UV-optical colour correlates with both luminosity and redshift such that galaxies at lower redshift and higher luminosity are typically redder. Assuming that the escape fraction of ionizing photons is close to zero, the effect of nebular emission is to redden the UV-optical 1500 - Vw colour by, on average, 0.4 mag at z = 8 declining to 0.25 mag at z = 4. Young and low-metallicity stellar populations, which typically have bluer pure stellar UV-optical colours, produce larger ionizing luminosities and are thus more strongly affected by the reddening effects of nebular emission. This causes the distribution of 1500 - Vw colours to narrow and the trends with luminosity and redshift to weaken. The strong effect of nebular emission leaves observed-frame colours critically sensitive to the redshift of the source. For example, increasing the redshift by 0.1 can result in observed-frame colours changing by up to ˜0.6. These predictions reinforce the need to include nebular emission when modelling the spectral energy distributions of galaxies at high redshift and also highlight the difficultly in interpreting the observed colours of individual galaxies without precise redshift information.

Wilkins, Stephen M.; Coulton, William; Caruana, Joseph; Croft, Rupert; Matteo, Tiziana Di; Khandai, Nishikanta; Feng, Yu; Bunker, Andrew; Elbert, Holly

2013-11-01

332

An evaluation of a computer code based on linear acoustic theory for predicting helicopter main rotor noise  

Microsoft Academic Search

Acoustic characteristics predicted using a recently developed computer code were correlated with measured acoustic data for two helicopter rotors. The analysis, is based on a solution of the Ffowcs-Williams-Hawkings (FW-H) equation and includes terms accounting for both the thickness and loading components of the rotational noise. Computations are carried out in the time domain and assume free field conditions. Results

S. J. Davis; T. A. Egolf

1980-01-01

333

On the system level prediction of joint time frequency spreading systems with carrier phase noise  

Microsoft Academic Search

Phase noise is a topic of theoretical and practical interest in electronic circuits. Although progress has been made in the characterization of its description, there are still considerable gaps in its effects especially on multi-carrier spreading systems. In this paper, we investigate the impact of a local oscillator phase noise on the multi-carrier 2 dimensional (2D) spreading systems based on

Youssef Nasser; Mathieu Des Noes; Laurent Ros; Geneviève Jourdain

2010-01-01

334

Prediction of Turbulence-Generated Noise in Unheated Jets. Part 1; JeNo Technical Manual (Version 1.0)  

NASA Technical Reports Server (NTRS)

The model-based approach, used by the JeNo code to predict jet noise spectral directivity, is described. A linearized form of Lilley's equation governs the non-causal Green s function of interest, with the non-linear terms on the right hand side identified as the source. A Reynolds-averaged Navier-Stokes (RANS) solution yields the required mean flow for the solution of the propagation Green s function in a locally parallel flow. The RANS solution also produces time- and length-scales needed to model the non-compact source, the turbulent velocity correlation tensor, with exponential temporal and spatial functions. It is shown that while an exact non-causal Green s function accurately predicts the observed shift in the location of the spectrum peak with angle as well as the angularity of sound at low to moderate Mach numbers, the polar directivity of radiated sound is not entirely captured by this Green s function at high subsonic and supersonic acoustic Mach numbers. Results presented for unheated jets in the Mach number range of 0.51 to 1.8 suggest that near the peak radiation angle of high-speed jets, a different source/Green s function convolution integral may be required in order to capture the peak observed directivity of jet noise. A sample Mach 0.90 heated jet is also discussed that highlights the requirements for a comprehensive jet noise prediction model.

Khavaran, Abbas; Bridges, James; Georgiadis, Nicholas

2005-01-01

335

GENERAL: GEKF, GUKF and GGPF based prediction of chaotic time-series with additive and multiplicative noises  

NASA Astrophysics Data System (ADS)

On the assumption that random interruptions in the observation process are modelled by a sequence of independent Bernoulli random variables, this paper generalize the extended Kalman filtering (EKF), the unscented Kalman filtering (UKF) and the Gaussian particle filtering (GPF) to the case in which there is a positive probability that the observation in each time consists of noise alone and does not contain the chaotic signal (These generalized novel algorithms are referred to as GEKF, GUKF and GGPF correspondingly in this paper). Using weights and network output of neural networks to constitute state equation and observation equation for chaotic time-series prediction to obtain the linear system state transition equation with continuous update scheme in an online fashion, and the prediction results of chaotic time series represented by the predicted observation value, these proposed novel algorithms are applied to the prediction of Mackey-Glass time-series with additive and multiplicative noises. Simulation results prove that the GGPF provides a relatively better prediction performance in comparison with GEKF and GUKF.

Wu, Xue-Dong; Song, Zhi-Huan

2008-09-01

336

CMOS front-end amplifier for broadband DTV tuner  

E-print Network

In this work, the design of a CMOS broadband low noise amplifier with inherent high performance single-to-differential conversion is presented. These characteristics are driven by the double quadrature single conversion digital television tuner...

Zhang, Guang

2005-08-29

337

High speed propeller performance and noise predictions at takeoff/landing conditions  

NASA Astrophysics Data System (ADS)

The performance and noise of a high speed SR-7A model propeller under takeoff/landing conditions are considered. The blade loading distributions are obtained by solving the three-dimensional Euler equations and the sound pressure levels are computed using a time domain approach. At the nominal takeoff operating point, the blade sections near the hub are lightly or negatively loaded. The chordwise loading distributions are distinctly different from those of cruise conditions. The noise of the SR-7A model propeller at takeoff is dominated by the loading noise, similar to that at cruise conditions. The waveforms of the acoustic pressure signature are nearly sinusoidal in the plane of the propeller. The computed directivity of the blade passing frequency tone agrees fairly well with the data at nominal takeoff blade angle.

Nallasamy, M.; Woodward, R. P.; Groeneweg, J. F.

1988-01-01

338

High speed propeller performance and noise predictions at takeoff/landing conditions  

NASA Astrophysics Data System (ADS)

The performance and noise of a high speed SR-7A model propeller under takeoff/landing conditions are considered. The blade loading distributions are obtained by solving the three-dimensional Euler equations and the sound pressure levels are computed using a time domain approach. At the nominal takeoff operating point, the blade sections near the hub are lightly or negatively loaded. The chordwise loading distributions are distinctly different from those of cruise conditions. The noise of the SR-7A model propeller at takeoff is dominated by the loading noise, similar to that at cruise conditions. The waveforms of the acoustic pressure signature are nearly sinusoidal in the plane of the propeller. The computed directivity of the blade passing frequency tone agrees fairly well with the data at nominal takeoff blade angle.

Nallasamy, M.; Woodward, R. P.; Groeneweg, J. F.

1987-01-01

339

The uses and abuses of the acoustic analogy in helicopter rotor noise prediction  

NASA Technical Reports Server (NTRS)

The generation of noise by helicopter rotor blades is considered theoretically, reviewing recent analyses based on the acoustic analogy (where the effect of fluid motion is replaced by fictitious sources in an undisturbed fluid). The fundamental principles of the acoustic approach are explained and illustrated with diagrams; the governing Ffowcs-Williams/Hawkings equations are written with a reformulated quadrupole term; and the directivity of noise produced (1) by regions with steep gradients (such as shock surfaces) and (2) by boundary-layer quadrupoles (tip-vortex and blade wakes) is shown to be the same as that of thickness noise. The need to include both (1) and (2) in acoustic-analogy computations is indicated.

Farassat, F.; Brentner, Kenneth S.

1987-01-01

340

An Integrated Low-Speed Performance and Noise Prediction Methodology for Subsonic Aircraft  

NASA Technical Reports Server (NTRS)

An integrated methodology has been assembled to compute the engine performance, takeoff and landing trajectories, and community noise levels for a subsonic commercial aircraft. Where feasible, physics-based noise analysis methods have been used to make the results more applicable to newer, revolutionary designs and to allow for a more direct evaluation of new technologies. The methodology is intended to be used with approximation methods and risk analysis techniques to allow for the analysis of a greater number of variable combinations while retaining the advantages of physics-based analysis. Details of the methodology are described and limited results are presented for a representative subsonic commercial aircraft.

Olson, E. D.; Mavris, D. N.

2000-01-01

341

Noncausal f-x-y regularized nonstationary prediction filtering for random noise attenuation on 3D seismic data  

NASA Astrophysics Data System (ADS)

Seismic noise attenuation is very important for seismic data analysis and interpretation, especially for 3D seismic data. In this paper, we propose a novel method for 3D seismic random noise attenuation by applying noncausal regularized nonstationary autoregression (NRNA) in f-x-y domain. The proposed method, 3D NRNA (f-x-y domain) is the extended version of 2D NRNA (f-x domain). f-x-y NRNA can adaptively estimate seismic events of which slopes vary in 3D space. The key idea of this paper is to consider that the central trace can be predicted by all around this trace from all directions in 3D seismic cube, while the 2D f-x NRNA just considers that the middle trace can be predicted by adjacent traces along one space direction. 3D f-x-y NRNA uses more information from circumjacent traces than 2D f-x NRNA to estimate signals. Shaping regularization technology guarantees that the nonstationary autoregression problem can be realizable in mathematics with high computational efficiency. Synthetic and field data examples demonstrate that, compared with f-x NRNA method, f-x-y NRNA can be more effective in suppressing random noise and improve trace-by-trace consistency, which are useful in conjunction with interactive interpretation and auto-picking tools such as automatic event tracking.

Liu, Guochang; Chen, Xiaohong

2013-06-01

342

A prediction method for separating and quantifying noise contributions from casings and other plate like components in complex machines  

NASA Astrophysics Data System (ADS)

In the context of noise source identification in machines, sound intensity, pressure or velocity distributions on a plane in space are commonly provided by intensity or holography maps. These maps, however, are not capable of separating the sources that are located on different planes, e.g. machines' radiating casings versus internal noise sources. The method discussed in this paper has been developed to analyze such situations. It consists of multiple partially coherent inputs-single output modeling to predict the radiations generated by machine casings or other plate like components. A parallel analysis with intensity will then enable to separate the casing or plate contribution from those of the internal sources. The application of this technique must, however, be accompanied by tools that allow to check its validity. Several of such tools are suggested. The method applications and validity checks have been discussed for a grinder wheel guard and a panel saw's blade casing.

Nejade, A.

2012-11-01

343

Application of system engineering processes to analyze and predict engine cooling fan system noise for off-highway machines  

NASA Astrophysics Data System (ADS)

System Engineering processes were applied to create a Cooling Fan System Noise Analysis Tool for a back-hoe loader machine. The Cooling Fan System Noise Analysis Tool combined elements of aeroacoustic theory, Fan Law, sound power measurements and particle image velocimetry into a single computer analysis tool. The cooling fan system consisted of a cooling fan, multiple radiators in front of the cooling fan, a shroud, a mock engine behind the cooling fan, and a simulated engine compartment. A vortex flow structure was measured in front of the cooling fan. The cooling fan system sound power spectrum was measured. The radiated sound power spectrum for the vortex interaction with the fan blades was calculated. Measured and predicted cooling fan system sound power results were compared. The overall structure and approach will be presented along with an overview of the theory and initial results.

Masini, Christopher P.; Mann, J. Adin

2005-09-01

344

The importance of quadrupole sources in prediction of transonic tip speed propeller noise  

Microsoft Academic Search

A theoretical analysis is presented for the harmonic noise of high speed, open rotors. Far field acoustic radiation equations based on the Ffowcs Williams\\/Hawkings theory are derived for a static rotor with thin blades and zero lift. Near the plane of rotation, the dominant sources are the volume displacement and the varrhou2 quadrupole, where u is the disturbance velocity component

D. B. Hanson; M. R. Fink

1979-01-01

345

The importance of quadrupole sources in prediction of transonic tip speed propeller noise  

Microsoft Academic Search

A theoretical analysis is presented for the harmonic noise of high speed, open rotors. Far field acoustic radiation equations based on the Ffowcs-Williams\\/Hawkings theory are derived for a static rotor with thin blades and zero lift. Near the plane of rotation, the dominant sources are the volume displacement and the rho U(2) quadrupole, where u is the disturbance velocity component

D. B. Hanson; M. R. Fink

1978-01-01

346

Effect of Coannular Flow on Linearized Euler Equation Predictions of Jet Noise  

NASA Technical Reports Server (NTRS)

An improved version of a previously validated linearized Euler equation solver is used to compute the noise generated by coannular supersonic jets. Results for a single supersonic jet are compared to the results from both a normal velocity profile and an inverted velocity profile supersonic jet.

Hixon, R.; Shih, S.-H.; Mankbadi, Reda R.

1997-01-01

347

Prediction of Work Efficiency in Early Adolescence under the Effects of Noise  

ERIC Educational Resources Information Center

This is a short summary of research on how different stress factors in the work environment (climate, light, noise) affect work performance of early adolescents. Due to the complexity of the measurements, the research consisted of a small sample of male adolescents (N = 20); average age 13.5 years (SD = 0.25). Tasks were used which demanded…

Fosnaric, Samo; Planinsec, Jurij

2008-01-01

348

Annoyance caused by advanced turboprop aircraft flyover noise: Comparison of different propeller configurations  

NASA Technical Reports Server (NTRS)

A laboratory experiment was conducted to compare the annoyance of flyover noise from advanced turboprop aircraft having different propeller configurations with the annoyance of conventional turboprop and turbofan aircraft flyover noise. A computer synthesis system was used to generate 40 realistic, time varying simulations of advanced turboprop takeoff noise. Of the 40 noises, single-rotating propeller configurations (8) and counter-rotating propeller configurations with an equal (12) and unequal (20) number of blades on each rotor were represented. Analyses found that advanced turboprops with single-rotating propellers were, on average, slightly less annoying than the other aircraft. Fundamental frequency and tone-to-broadband noise ratio affected annoyance response to advanced turboprops, but the effects varied with propeller configuration and noise metric. The addition of duration corrections and corrections for tones above 500 Hz to the noise measurement procedures improved annoyance prediction ability.

Mccurdy, David A.

1991-01-01

349

Rotor noise  

NASA Technical Reports Server (NTRS)

The physical characteristics and sources of rotorcraft noise as they exist today are presented. Emphasis is on helicopter-like vehicles, that is, on rotorcraft in nonaxial flight. The mechanisms of rotor noise are reviewed in a simple physical manner for the most dominant sources of rotorcraft noise. With simple models, the characteristic time- and frequency-domain features of these noise sources are presented for idealized cases. Full-scale data on several rotorcraft are then reviewed to allow for the easy identification of the type and extent of the radiating noise. Methods and limitations of using scaled models to test for several noise sources are subsequently presented. Theoretical prediction methods are then discussed and compared with experimental data taken under very controlled conditions. Finally, some promising noise reduction technology is reviewed.

Schmitz, F. H.

1991-01-01

350

Computational Aeroacoustics Cascade Model of Fan Noise  

Microsoft Academic Search

A Computational Aeroacoustics [CAA] cascade model has been built to study the generation and propagation mechanisms of noise resulting from the interaction of the fan and outlet guide vanes in a high-bypass ratio turbofan engine. Also called rotor-stator interaction noise, this noise source is a dominant contributor to the total tone and broadband noise levels produced by the engine, and

Philip Paul LePoudre

2011-01-01

351

Contributions of cochlea-scaled entropy and consonant-vowel boundaries to prediction of speech intelligibility in noise  

PubMed Central

Recent evidence suggests that spectral change, as measured by cochlea-scaled entropy (CSE), predicts speech intelligibility better than the information carried by vowels or consonants in sentences. Motivated by this finding, the present study investigates whether intelligibility indices implemented to include segments marked with significant spectral change better predict speech intelligibility in noise than measures that include all phonetic segments paying no attention to vowels/consonants or spectral change. The prediction of two intelligibility measures [normalized covariance measure (NCM), coherence-based speech intelligibility index (CSII)] is investigated using three sentence-segmentation methods: relative root-mean-square (RMS) levels, CSE, and traditional phonetic segmentation of obstruents and sonorants. While the CSE method makes no distinction between spectral changes occurring within vowels/consonants, the RMS-level segmentation method places more emphasis on the vowel-consonant boundaries wherein the spectral change is often most prominent, and perhaps most robust, in the presence of noise. Higher correlation with intelligibility scores was obtained when including sentence segments containing a large number of consonant-vowel boundaries than when including segments with highest entropy or segments based on obstruent/sonorant classification. These data suggest that in the context of intelligibility measures the type of spectral change captured by the measure is important. PMID:22559382

Chen, Fei; Loizou, Philipos C.

2012-01-01

352

Underwater radiated noise from modern commercial ships.  

PubMed

Underwater radiated noise measurements for seven types of modern commercial ships during normal operating conditions are presented. Calibrated acoustic data (<1000 Hz) from an autonomous seafloor-mounted acoustic recorder were combined with ship passage information from the Automatic Identification System. This approach allowed for detailed measurements (i.e., source level, sound exposure level, and transmission range) on ships of opportunity. A key result was different acoustic levels and spectral shapes observed from different ship-types. A 54 kGT container ship had the highest broadband source level at 188 dB re 1 ?Pa@1m; a 26 kGT chemical tanker had the lowest at 177 dB re 1 ?Pa@1m. Bulk carriers had higher source levels near 100 Hz, while container ship and tanker noise was predominantly below 40 Hz. Simple models to predict source levels of modern merchant ships as a group from particular ship characteristics (e.g., length, gross tonnage, and speed) were not possible given individual ship-type differences. Furthermore, ship noise was observed to radiate asymmetrically. Stern aspect noise levels are 5 to 10 dB higher than bow aspect noise levels. Collectively, these results emphasize the importance of including modern ship-types in quantifying shipping noise for predictive models of global, regional, and local marine environments. PMID:22280574

McKenna, Megan F; Ross, Donald; Wiggins, Sean M; Hildebrand, John A

2012-01-01

353

An Implicit Method for Data Prediction and Impulse Noise Removal from Corrupted Signals  

NASA Astrophysics Data System (ADS)

A robust and reliable implicit method is proposed for application in data interpolation. The algorithm is based on a recently developed analytic approximation method, namely the distributed approximating functionals (DAFs), which is known to have the ``well-tempered'' property of UNIFORMLY approximating a function and its derivatives. In comparison with the conventionally used local explicit interpolation algorithms, the implicit method achieves much more accurate interpolation results because it couples all sample values (both known and unknown) in the domain of interest using a set of simultaneous linear algebraic equations. Due to the fact that the well-tempered DAFs also are very good low-pass filters, the performance of the DAF-based implicit method is not affected very much by the high frequency noise in the input signal. As an application, the proposed algorithm is applied to signals that are corrupted with impulse noise.

Zhang, De S.; Wang, Haixiang; Kouri, Donald J.; Hoffman, David K.

354

Motor noise generation and prediction for high spinning speed hard disk drive  

Microsoft Academic Search

The acoustic level of a hard disk drive is an important specification. This is especially so for enterprise HDD which is required\\u000a to operate under a high spinning speed. In order to reduce the acoustics level of a HDD, an in depth understanding behind\\u000a the mechanisms whereby the noise is being generated in a HDD should be established. This paper

F. Gao; W. Z. Lin; C. W. Lee; H. N. Phyu; J. Q. Mou; E. H. Ong

2011-01-01

355

Aircraft Conceptual Design and Risk Analysis Using Physics-Based Noise Prediction  

NASA Technical Reports Server (NTRS)

An approach was developed which allows for design studies of commercial aircraft using physics-based noise analysis methods while retaining the ability to perform the rapid trade-off and risk analysis studies needed at the conceptual design stage. A prototype integrated analysis process was created for computing the total aircraft EPNL at the Federal Aviation Regulations Part 36 certification measurement locations using physics-based methods for fan rotor-stator interaction tones and jet mixing noise. The methodology was then used in combination with design of experiments to create response surface equations (RSEs) for the engine and aircraft performance metrics, geometric constraints and take-off and landing noise levels. In addition, Monte Carlo analysis was used to assess the expected variability of the metrics under the influence of uncertainty, and to determine how the variability is affected by the choice of engine cycle. Finally, the RSEs were used to conduct a series of proof-of-concept conceptual-level design studies demonstrating the utility of the approach. The study found that a key advantage to using physics-based analysis during conceptual design lies in the ability to assess the benefits of new technologies as a function of the design to which they are applied. The greatest difficulty in implementing physics-based analysis proved to be the generation of design geometry at a sufficient level of detail for high-fidelity analysis.

Olson, Erik D.; Mavris, Dimitri N.

2006-01-01

356

Broadband monopole optical nano-antennas  

NASA Astrophysics Data System (ADS)

In this paper, a novel design of broadband monopole optical nano-antennas is proposed. It consists of a corrugated halfelliptical patch inside an elliptical aperture. Full-wave electromagnetic simulations have been used to investigate the performance of the nano-antenna. The predicted performance of the proposed monopole nano-antenna is remarkably broadband. Moreover, the proposed broadband nano-antenna can respond to light waves with different polarizations. The proposed optical antenna will pave the way towards the development of high performance optical antennas and optical systems.

Zhou, Rongguo; Ding, Jun; Arigong, Bayaner; Lin, Yuankun; Zhang, Hualiang

2014-03-01

357

Analytical prediction of the interior noise for cylindrical models of aircraft fuselages for prescribed exterior noise fields. Phase 2: Models for sidewall trim, stiffened structures and cabin acoustics with floor partition  

NASA Technical Reports Server (NTRS)

An airplane interior noise prediction model is developed to determine the important parameters associated with sound transmission into the interiors of airplanes, and to identify apropriate noise control methods. Models for stiffened structures, and cabin acoustics with floor partition are developed. Validation studies are undertaken using three test articles: a ring stringer stiffened cylinder, an unstiffened cylinder with floor partition, and ring stringer stiffened cylinder with floor partition and sidewall trim. The noise reductions of the three test articles are computed using the heoretical models and compared to measured values. A statistical analysis of the comparison data indicates that there is no bias in the predictions although a substantial random error exists so that a discrepancy of more than five or six dB can be expected for about one out of three predictions.

Pope, L. D.; Wilby, E. G.

1982-01-01

358

Computation of Supersonic Jet Mixing Noise Using PARC Code With a kappa-epsilon Turbulence Model  

NASA Technical Reports Server (NTRS)

A number of modifications have been proposed in order to improve the jet noise prediction capabilities of the MGB code. This code which was developed at General Electric, employees the concept of acoustic analogy for the prediction of turbulent mixing noise. The source convection and also refraction of sound due to the shrouding effect of the mean flow are accounted for by incorporating the high frequency solution to Lilley's equation for cylindrical jets (Balsa and Mani). The broadband shock-associated noise is estimated using Harper-Bourne and Fisher's shock noise theory. The proposed modifications are aimed at improving the aerodynamic predictions (source/spectrum computations) and allowing for the non- axisymmetric effects in the jet plume and nozzle geometry (sound/flow interaction). In addition, recent advances in shock noise prediction as proposed by Tam can be employed to predict the shock-associated noise as an addition to the jet mixing noise when the flow is not perfectly expanded. Here we concentrate on the aerodynamic predictions using the PARC code with a k-E turbulence model and the ensuing turbulent mixing noise. The geometry under consideration is an axisymmetric convergent-divergent nozzle at its design operating conditions. Aerodynamic and acoustic computations are compared with data as well as predictions due to the original MGB model using Reichardt's aerodynamic theory.

Khavaran, A.; Kim, C. M.

1999-01-01

359

Hearing through the noise: Predictability and tipping points in the climate  

NASA Astrophysics Data System (ADS)

It is taken for granted that the limited predictability in the initial value problem, the weather prediction, and the predictability of the statistics are two distinct problems. Predictability of the first kind in a chaotic dynamical system is limited due to critical dependence on initial conditions. Predictability of the second kind is possible in an ergodic system, where either the dynamics is known and the phase space attractor can be characterized by simulation or the system can be observed for such long times that the statistics can be obtained from temporal averaging, assuming that the attractor does not change in time. For the climate system the distinction between predictability of the first and the second kind is fuzzy. On the one hand, weather prediction is not related to the inverse of the Lyapunov exponent of the system, determined by the much shorter times in the turbulent boundary layer. These time scales are effectively averaged on the time scales of the flow in the free atmosphere. On the other hand, turning to climate change predictions, the time scales on which the system is considered quasi-stationary, such that the statistics can be predicted as a function of an external parameter, say atmospheric CO2, is still short in comparison to slow oceanic dynamics. On these time scales the state of these slow variables still depends on the initial conditions. This fuzzy distinction between predictability of the first and of the second kind is related to the lack of scale separation between fast and slow components of the climate system. The non-linear nature of the problem furthermore opens the possibility of multiple attractors, or multiple quasi-steady states. As the paleoclimatic record shows, the climate has been jumping between different quasi-stationary climates. The question is: Can such tipping points be predicted? This is a new kind of predictability (the third kind). The Dansgaard-Oeschger climate events observed in ice core records are analyzed in order to answer some of these questions. The result of the analysis points to a fundamental limitation in predictability of the third kind. References: P. D. Ditlevsen and S. Johnsen, Geophys. Res. Lett., 37, L19703, 2010 Peter D. Ditlevsen, Contemporary Physics, 50, 511-532, 2009 P. D. Ditlevsen, H. Svensmark and S. Johnsen, Nature 379, 810-812, 1996

Ditlevsen, Peter

2014-05-01

360

Evaluation of the annoyance due to helicopter rotor noise  

NASA Technical Reports Server (NTRS)

A program was conducted in which 25 test subjects adjusted the levels of various helicopter rotor spectra until the combination of the harmonic noise and a broadband background noise was judged equally annoying as a higher level of the same broadband noise spectrum. The subjective measure of added harmonic noise was equated to the difference in the two levels of broadband noise. The test participants also made subjective evaluations of the rotor noise signatures which they created. The test stimuli consisted of three degrees of rotor impulsiveness, each presented at four blade passage rates. Each of these 12 harmonic sounds was combined with three broadband spectra and was adjusted to match the annoyance of three different sound pressure levels of broadband noise. Analysis of variance indicated that the important variables were level and impulsiveness. Regression analyses indicated that inclusion of crest factor improved correlation between the subjective measures and various objective or physical measures.

Sternfeld, H., Jr.; Doyle, L. B.

1978-01-01

361

Contribution of tonal components to the overall loudness, annoyance and noisiness of noise: Relation between single tones and noise spectral shape  

NASA Technical Reports Server (NTRS)

A large scale laboratory investigation of loudness, annoyance, and noisiness produced by single-tone-noise complexes was undertaken to establish a broader data base for quanitification and prediction of perceived annoyance of sounds containing tonal components. Loudness, annoyance, and noisiness were distinguished as separate, distinct, attributes of sound. Three different spectral patterns of broadband noise with and without added tones were studied: broadband-flat, low-pass, and high-pass. Judgments were obtained by absolute magnitude estimation supplement by loudness matching. The data were examined and evaluated to determine the potential effects of (1) the overall sound pressure level (SPL) of the noise-tone complex, (2) tone SPL, (3) noise SPL, (4) tone-to-noise ratio, (5) the frequency of the added tone, (6) noise spectral shape, and (7) subjective attribute judged on absolute magnitude of annoyance. Results showed that, in contrast to noisiness, loudness and annoyance growth behavior depends on the relationship between the frequency of the added tone and the spectral shape of the noise. The close correspondence between the frequency of the added tone and the spectral shape of the noise. The close correspondence between loundness and annoyance suggests that, to better understand perceived annoyance of sound mixtures, it is necessary to relate the results to basic auditory mechanisms governing loudness and masking.

Hellman, R. P.

1985-01-01

362

Results from two studies in seismology: I. Seismic observations and modeling in the Santa Clara Valley, California. II. Observations and removal of the long-period noise at the Monterey ocean bottom broadband station (MOBB)  

NASA Astrophysics Data System (ADS)

Results from two projects are presented in this work. Following brief introductory Chapter 1 that provides general background, Chapter 2 describes the influence of the Santa Clara Valley (SCV) basin structure on the propagation of teleseismic waves. Teleseismic P-waves recorded during the 1998 deployment of the 41-station seismic array are used in the analysis. Observations are compared to synthetics computed by 3D finite-difference simulations using the University of California, Berkeley (UCB) and the U.S. Geological Survey (USGS) 3D velocity models. Chapter 3 includes further study of the ground-motion amplification in the SCV using microseisms recorded by the SCV seismic array in 1998. The obtained results are compared to the local earthquake amplification. Chapter 4 presents results of the 3D simulations using the most recent version of the USGS velocity model for the greater San Francisco Bay Area. Results are compared to 1998 SCV seismic array observations and to simulations presented in Chapter 2. Results presented in Chapters 2 to 4 all show strong correlations between basin depth reported in the USGS 3D seismic velocity model and different relative measures of ground motion parameters. The teleseismic, local earthquake and microseism observations are also found to be strongly correlated with one another. Since the results suggest that all three datasets are sensitive to the basin structure, they can be used to improve the 3D velocity model. I started to develop a simultaneous inversion of the teleseismic, local, and microseism observations to refine the seismic velocity model. Chapter 5 presents preliminary results and future plans. Results from the second project are included in Chapters 6 to 9. Chapter 6 provides information about the Monterey ocean bottom broadband seismic station (MOBB). It explains why seismology is moving into the oceans, describes the MOBB location, provides details about the instruments that comprise the MOBB, and describes the deployment. Examples of data and preliminary analysis are also included. Chapter 7 presents observations of infragravity waves at MOBB. Combined with the information from the ocean buoys, the MOBB data show that the infragravity waves in the longer than 20 s period band are mainly locally generated from shorter-period ocean waves. Two types of the observed infragravity band signal modulation are presented and possible mechanisms for the modulation are discussed. Also included is the analysis of the ocean bottom seismic data from the temporary Oregon ULF/VLF deployment that also indicates that the infragravity waves are primarily locally generated. Chapter 8 describes analysis of data from another ocean bottom station. KEBB is located offshore Washington, in deeper water and further offshore than MOBB. Results suggests that in this case the infragravity waves are generated from shorter period ocean waves in the coastal region and not locally at KEBB. Chapter 9 focuses on the removal of the long-period background as well as signal-generated noise from the MOBB data. Methods used to improve signal-to-noise ratio for the ocean bottom seismic data are presented.

Dolenc, David

363

TFaNS Tone Fan Noise Design/Prediction System. Volume 1; System Description, CUP3D Technical Documentation and Manual for Code Developers  

NASA Technical Reports Server (NTRS)

TFaNS is the Tone Fan Noise Design/Prediction System developed by Pratt & Whitney under contract to NASA Lewis (presently NASA Glenn). The purpose of this system is to predict tone noise emanating from a fan stage including the effects of reflection and transmission by the rotor and stator and by the duct inlet and nozzle. These effects have been added to an existing annular duct/isolated stator noise prediction capability. TFaNS consists of: The codes that compute the acoustic properties (reflection and transmission coefficients) of the various elements and write them to files. Cup3D: Fan Noise Coupling Code that reads these files, solves the coupling problem, and outputs the desired noise predictions. AWAKEN: CFD/Measured Wake Postprocessor which reformats CFD wake predictions and/or measured wake data so it can be used by the system. This volume of the report provides technical background for TFaNS including the organization of the system and CUP3D technical documentation. This document also provides information for code developers who must write Acoustic Property Files in the CUP3D format. This report is divided into three volumes: Volume I: System Description, CUP3D Technical Documentation, and Manual for Code Developers; Volume II: User's Manual, TFaNS Vers. 1.4; Volume III: Evaluation of System Codes.

Topol, David A.

1999-01-01

364

Noise reduction in supersonic jets by nozzle fluidic inserts  

NASA Astrophysics Data System (ADS)

Professor Philip Doak spent a very productive time as a consultant to the Lockheed-Georgia Company in the early 1970s. The focus of the overall research project was the prediction and reduction of noise from supersonic jets. Now, 40 years on, the present paper describes an innovative methodology and device for the reduction of supersonic jet noise. The goal is the development of a practical active noise reduction technique for low bypass ratio turbofan engines. This method introduces fluidic inserts installed in the divergent wall of a CD nozzle to replace hard-wall corrugation seals, which have been demonstrated to be effective by Seiner (2005) [1]. By altering the configuration and operating conditions of the fluidic inserts, active noise reduction for both mixing and shock noise has been obtained. Substantial noise reductions have been achieved for mixing noise in the maximum noise emission direction and in the forward arc for broadband shock-associated noise. To achieve these reductions (on the order of greater than 4 and 2 dB for the two main components respectively), practically achievable levels of injection mass flow rates have been used. The total injected mass flow rates are less than 4% of the core mass flow rate and the effective operating injection pressure ratio has been maintained at or below the same level as the nozzle pressure ratio of the core flow.

Morris, Philip J.; McLaughlin, Dennis K.; Kuo, Ching-Wen

2013-08-01

365

Workshop on Jet Exhaust Noise Reduction for Tactical Aircraft - NASA Perspective  

NASA Technical Reports Server (NTRS)

Jet noise from supersonic, high performance aircraft is a significant problem for takeoff and landing operations near air bases and aircraft carriers. As newer aircraft with higher thrust and performance are introduced, the noise tends to increase due to higher jet exhaust velocities. Jet noise has been a subject of research for over 55 years. Commercial subsonic aircraft benefit from changes to the engine cycle that reduce the exhaust velocities and result in significant noise reduction. Most of the research programs over the past few decades have concentrated on commercial aircraft. Progress has been made by introducing new engines with design features that reduce the noise. NASA has recently started a new program called "Fundamental Aeronautics" where three projects (subsonic fixed wing, subsonic rotary wing, and supersonics) address aircraft noise. For the supersonics project, a primary goal is to understand the underlying physics associated with jet noise so that improved noise prediction tools and noise reduction methods can be developed for a wide range of applications. Highlights from the supersonics project are presented including prediction methods for broadband shock noise, flow measurement methods, and noise reduction methods. Realistic expectations are presented based on past history that indicates significant jet noise reduction cannot be achieved without major changes to the engine cycle. NASA s past experience shows a few EPNdB (effective perceived noise level in decibels) can be achieved using low noise design features such as chevron nozzles. Minimal thrust loss can be expected with these nozzles (< 0.5%) and they may be retrofitted on existing engines. In the long term, it is desirable to use variable cycle engines that can be optimized for lower jet noise during takeoff operations and higher thrust for operational performance. It is also suggested that noise experts be included early in the design process for engine nozzle systems to participate in decisions that may impact the jet noise.

Huff, Dennis L.; Henderson, Brenda S.

2007-01-01

366

Optimal launch power prediction of a 100G PM-DQPSK dispersion-managed link with the Gaussian noise model  

NASA Astrophysics Data System (ADS)

Of all the non-linear fiber propagation models proposed over the years, the Gaussian Noise (GN) model is growing in popularity due to its simplicity and yet reliability when it comes to predict performance of uncompensated coherent transmission (UT) systems that rely on state-of-the art digital-signal processing (DSP) for dispersion compensation. However, many of the systems currently deployed rely on optical CD compensation. Overhauling or upgrading these systems with the most recent DSP is not always feasible. In this context, it is important to broad the range of the GNmodel to dispersion managed (DM) systems, so both scenarios can benefit from a low complexity, fast and reliable performance prediction tool. In this paper, we validate the first results comparing the performance in both accuracy and simulation time of the GN model simulating a realistic DM scenario that relies on periodical spans of non-dispersion shifted fiber (NDSF) to perform the dispersion compensation. The same realistic scenarios were modeled with commercial software and the GN model. The objective was to predict the optimal launch power for different link lengths, central wavelengths and channel spacing values. Preliminary results obtained with the GN model are in good agreement with the ones from the commercial software for several link distances tested up to 2400 Km.

Almeida, Telmo P.; Drummond, Miguel V.; Pavlovi?, Natasa B.; André, Paulo S.; Nogueira, Rogério N.

2014-08-01

367

A method for predicting the noise levels of coannular jets with inverted velocity profiles  

NASA Technical Reports Server (NTRS)

A coannular jet was equated with a single stream equivalent jet with the same mass flow, energy, and thrust. The acoustic characteristics of the coannular jet were then related to the acoustic characteristics of the single jet. Forward flight effects were included by incorporating a forward exponent, a Doppler amplification factor, and a Strouhal frequency shift. Model test data, including 48 static cases and 22 wind tunnel cases, were used to evaluate the prediction method. For the static cases and the low forward velocity wind tunnel cases, the spectral mean square pressure correlation coefficients were generally greater than 90 percent, and the spectral sound pressure level standard deviation were generally less than 3 decibels. The correlation coefficient and the standard deviation were not affected by changes in equivalent jet velocity. Limitations of the prediction method are also presented.

Russell, J. W.

1979-01-01

368

An evaluation of a computer code based on linear acoustic theory for predicting helicopter main rotor noise. [CH-53A and S-76 helicopters  

NASA Technical Reports Server (NTRS)

Acoustic characteristics predicted using a recently developed computer code were correlated with measured acoustic data for two helicopter rotors. The analysis, is based on a solution of the Ffowcs-Williams-Hawkings (FW-H) equation and includes terms accounting for both the thickness and loading components of the rotational noise. Computations are carried out in the time domain and assume free field conditions. Results of the correlation show that the Farrassat/Nystrom analysis, when using predicted airload data as input, yields fair but encouraging correlation for the first 6 harmonics of blade passage. It also suggests that although the analysis represents a valuable first step towards developing a truly comprehensive helicopter rotor noise prediction capability, further work remains to be done identifying and incorporating additional noise mechanisms into the code.

Davis, S. J.; Egolf, T. A.

1980-01-01

369

Jet Noise Research at NASA  

NASA Technical Reports Server (NTRS)

A presentation outlining current jet noise work at NASA was given at the NAVAIR Noise Workshop. Jet noise tasks in the Supersonics project of the Fundamental Aeronautics program were highlighted. The presentation gave an overview of developing jet noise reduction technologies and noise prediction capabilities. Advanced flow and noise diagnostic tools were also presented.

Henderson, Brenda

2008-01-01

370

NASA/Army supported noise source/noise reduction programs at Langley  

NASA Technical Reports Server (NTRS)

The helicopter noise research related to noise source mechanism identification and reduction includes many of the critical noise problems experienced by the helicopter. These include blade vortex interaction (BVI) noise, broadband turbulence ingestion noise, rotor blade self noise including trailing edge effects, model scale effects evaluations, and to some degree main rotor/tail rotor interaction noise. Issues that arise from this evaluation are; (1) Broadband noise can be a significant contribution to the overall noise problem. (2) Scale model investigations are an effective means of conducting helicopter noise research; however, more model/flight correlation studies are required to develop a high degree of confidence of the use of scale model results in the design process of helicopters. (3) More detailed investigations identifying critical factors affecting the main rotor/tail rotor noise mechanism are required.

Hoad, D. R.

1982-01-01

371

Comparison of Model Prediction with Measurements of Galactic Background Noise at L-Band  

NASA Technical Reports Server (NTRS)

The spectral window at L-band (1.413 GHz) is important for passive remote sensing of surface parameters such as soil moisture and sea surface salinity that are needed to understand the hydrological cycle and ocean circulation. Radiation from celestial (mostly galactic) sources is strong in this window and an accurate accounting for this background radiation is often needed for calibration. Modem radio astronomy measurements in this spectral window have been converted into a brightness temperature map of the celestial sky at L-band suitable for use in correcting passive measurements. This paper presents a comparison of the background radiation predicted by this map with measurements made with several modem L-band remote sensing radiometers. The agreement validates the map and the procedure for locating the source of down-welling radiation.

LeVine, David M.; Abraham, Saji; Kerr, Yann H.; Wilson, Willam J.; Skou, Niels; Sobjaerg, S.

2004-01-01

372

Prediction of Turbulence-Generated Noise in Unheated Jets. Part 2; JeNo Users' Manual (Version 1.0)  

NASA Technical Reports Server (NTRS)

JeNo (Version 1.0) is a Fortran90 computer code that calculates the far-field sound spectral density produced by axisymmetric, unheated jets at a user specified observer location and frequency range. The user must provide a structured computational grid and a mean flow solution from a Reynolds-Averaged Navier Stokes (RANS) code as input. Turbulence kinetic energy and its dissipation rate from a k-epsilon or k-omega turbulence model must also be provided. JeNo is a research code, and as such, its development is ongoing. The goal is to create a code that is able to accurately compute far-field sound pressure levels for jets at all observer angles and all operating conditions. In order to achieve this goal, current theories must be combined with the best practices in numerical modeling, all of which must be validated by experiment. Since the acoustic predictions from JeNo are based on the mean flow solutions from a RANS code, quality predictions depend on accurate aerodynamic input.This is why acoustic source modeling, turbulence modeling, together with the development of advanced measurement systems are the leading areas of research in jet noise research at NASA Glenn Research Center.

Khavaran, Abbas; Wolter, John D.; Koch, L. Danielle

2009-01-01

373

Jet noise modification by the 'whistler nozzle'  

NASA Technical Reports Server (NTRS)

The farfield noise characteristics of a subsonic whistler nozzle jet are measured as a function of Mach number (0.25, 0.37, and, 0.51), emission angle, and excitation mode. It is shown that a whistler nozzle has greater total and broadband acoustic power than an excited contraction nozzle; and that the intensity of far-field noise is a function of emission angle, Mach number, and whistler excitation stage. The whistler nozzle excitation produces broadband noise amplification with constant spectral shape; the broadband noise amplification (without associated whistler tones and harmonics) increases omnidirectionally with emission angle at all Mach numbers; and the broadband amplification factor decreases as Mach number and emission angle increase. Finally the whistler nozzle is described as a very efficient but inexpensive siren with applications in not only jet excitation but also acoustics.

Hasan, M. A. Z.; Islam, O.; Hussain, A. K. M. F.

1984-01-01

374

Relationship between container ship underwater noise levels and ship design, operational and oceanographic conditions  

PubMed Central

Low-frequency ocean ambient noise is dominated by noise from commercial ships, yet understanding how individual ships contribute deserves further investigation. This study develops and evaluates statistical models of container ship noise in relation to design characteristics, operational conditions, and oceanographic settings. Five-hundred ship passages and nineteen covariates were used to build generalized additive models. Opportunistic acoustic measurements of ships transiting offshore California were collected using seafloor acoustic recorders. A 5–10?dB range in broadband source level was found for ships depending on the transit conditions. For a ship recorded multiple times traveling at different speeds, cumulative noise was lowest at 8?knots, 65% reduction in operational speed. Models with highest predictive power, in order of selection, included ship speed, size, and time of year. Uncertainty in source depth and propagation affected model fit. These results provide insight on the conditions that produce higher levels of underwater noise from container ships.

McKenna, Megan F.; Wiggins, Sean M.; Hildebrand, John A.

2013-01-01

375

Relationship between container ship underwater noise levels and ship design, operational and oceanographic conditions  

NASA Astrophysics Data System (ADS)

Low-frequency ocean ambient noise is dominated by noise from commercial ships, yet understanding how individual ships contribute deserves further investigation. This study develops and evaluates statistical models of container ship noise in relation to design characteristics, operational conditions, and oceanographic settings. Five-hundred ship passages and nineteen covariates were used to build generalized additive models. Opportunistic acoustic measurements of ships transiting offshore California were collected using seafloor acoustic recorders. A 5-10 dB range in broadband source level was found for ships depending on the transit conditions. For a ship recorded multiple times traveling at different speeds, cumulative noise was lowest at 8 knots, 65% reduction in operational speed. Models with highest predictive power, in order of selection, included ship speed, size, and time of year. Uncertainty in source depth and propagation affected model fit. These results provide insight on the conditions that produce higher levels of underwater noise from container ships.

McKenna, Megan F.; Wiggins, Sean M.; Hildebrand, John A.

2013-05-01

376

Model-based prediction of long-term leaching of contaminants from secondary materials in road constructions and noise protection dams  

Microsoft Academic Search

In this study, contaminant leaching from three different secondary materials (demolition waste, munici- pal solid waste incineration ash, and blast furnace slag) to groundwater is assessed by numerical model- ing. Reactive transport simulations for a noise protection dam and a road dam (a typical German autobahn), in which secondary materials are reused as base layers, were performed to predict the

Christof Beyer; Wilfried Konrad; Hermann Rügner; Sebastian Bauer; Rudolf Liedl; Peter Grathwohl

2008-01-01

377

Metamaterial broadband angular selectivity  

E-print Network

We demonstrate how broadband angular selectivity can be achieved with stacks of one-dimensionally periodic photonic crystals, each consisting of alternating isotropic layers and effective anisotropic layers, where each ...

Shen, Yichen

378

Broadband waveguided light sources  

Microsoft Academic Search

In recent years, broadband fiber interferometers have become very popular as basic instruments used in optical low-coherence reflectometry for diagnostics of fiber and integrated optics devices or in optical coherence tomography (OCT) for imaging applications in the biomedical field. The longitudinal resolution of such instruments is inversely proportional to the optical bandwidth of the light source. Broadband luminescence from transition-metal-ion

M. Pollnau

2003-01-01

379

Rotorcraft Noise Model  

NASA Technical Reports Server (NTRS)

The Rotorcraft Noise Model (RNM) is an aircraft noise impact modeling computer program being developed for NASA-Langley Research Center which calculates sound levels at receiver positions either on a uniform grid or at specific defined locations. The basic computational model calculates a variety of metria. Acoustic properties of the noise source are defined by two sets of sound pressure hemispheres, each hemisphere being centered on a noise source of the aircraft. One set of sound hemispheres provides the broadband data in the form of one-third octave band sound levels. The other set of sound hemispheres provides narrowband data in the form of pure-tone sound pressure levels and phase. Noise contours on the ground are output graphically or in tabular format, and are suitable for inclusion in Environmental Impact Statements or Environmental Assessments.

Lucas, Michael J.; Marcolini, Michael A.

1997-01-01

380

RESEARCH ARTICLE The use of plasma actuators for bluff body broadband  

E-print Network

the attention of communities that live near airports to the problem of noise pollution (Raman and Mc (Crighton 1991; Macaraeg 1998). Since airframe noise is normally caused by the interactions betweenRESEARCH ARTICLE The use of plasma actuators for bluff body broadband noise control Yong Li · Xin

Huang, Xun

381

Prediction of jet mean flow structure in support of HSCT noise suppression concepts. [High Speed Civilian Transport  

NASA Technical Reports Server (NTRS)

The paper describes the application of techniques based on computational fluid dynamics to the simulation of jet flowfields. A solution code for the Reynolds-averaged Navier-Stokes equations is supplemented by conventional two-equation turbulence models based on the Boussinesq approximation. The axisymmetric SCIPVIS code is enhanced with the PARCH and CRAFT codes to examine plug-jet flowfields and imperfectly expanded axisymmetric free round jets. The sensitivity of shock/boundary layer interactions is observed in simulations of the plug case, and the adaptive gridding in the disk region and turbulence levels generated at the triple point are identified as areas in the Mach case that require improvement. Jet-wave structure in the region beyond the first several shock cells can be predicted, and turbulence modeling can be undertaken with respect to improving compressibility, length scale, vorticity, and energy budget. The mean flow structure of imperfectly expanded jets can be studied to develop related noise suppression concepts for the High-Speed Civilian Transport (HSCT).

Sinha, N.; Dash, S. M.; York, B. J.; Lee, R. A.

1991-01-01

382

Fourth Aircraft Interior Noise Workshop  

NASA Technical Reports Server (NTRS)

The fourth in a series of NASA/SAE Interior Noise Workshops was held on May 19 and 20, 1992. The theme of the workshop was new technology and applications for aircraft noise with emphasis on source noise prediction; cabin noise prediction; cabin noise control, including active and passive methods; and cabin interior noise procedures. This report is a compilation of the presentations made at the meeting which addressed the above issues.

Stephens, David G. (compiler)

1992-01-01

383

Jet Noise Research at NASA  

NASA Technical Reports Server (NTRS)

A presentation outlining current jet noise work at NASA was given to the Naval Research Advisory Committee. Jet noise tasks in the Supersonics project of the Fundamental Aeronautics program were highlighted. The presentation gave an overview of developing jet noise reduction technologies and noise prediction capabilities. Advanced flow and noise diagnostic tools were also presented.

Henderson, Brenda S.; Huff,Dennis

2009-01-01

384

An expert system for predicting the effects of speech interference due to noise pollution on humans using fuzzy approach  

Microsoft Academic Search

In this paper, an attempt has been made to develop an expert system using fuzzy approach to investigate the effects of noise pollution on speech interference. The speech interference measured in terms of speech intelligibility is considered to be a function of noise level, distance between speaker and listener, and the age of the listener. The main source of model

Zaheeruddin; V. K. Jain

2008-01-01

385

Assessing the effects of Tuned Vibration Absorbers (TVAs) on interior cabin noise levels: A correlation between analytical acoustic predictions and flight test measurements  

NASA Astrophysics Data System (ADS)

Analytical predictions of interior noise levels were correlated with actual flight test data obtained during a program undertaken to develop the proper design and optimal distribution of tuned vibration absorbers for the Dash-8 Series 300 aircraft. The measured operational deflection shape data of the fuselage structure were used as boundary conditions for the interior noise predictions using a boundary element method model and finite element method modal analysis. The analytical modelling procedures used to represent the interior cavity, the underlying assumptions on which the predictions were based, and the correlations obtained are reported. The main assumptions were that the fuselage model was closed with rigid end caps (simulating cabin bulkheads) and that the interior acoustic field was solely due to the vibration of the fuselage skin. In addition, a panel acoustic power contribution analysis was performed to identify the most heavily radiating panels. For example, the skin panels between frames 271 and 290 contributed 62 percent of the total radiated output power at 60 Hz. The flight data and noise predictions correlated well, showing decreased sound pressure levels within the cabin interior due to the effects of the tuned vibration absorbers.

Garcea, Ralph

386

Spectral tomography with diffuse near-infrared light: inclusion of broadband frequency domain spectral data  

PubMed Central

Near-infrared (NIR) region-based spectroscopy is examined for accuracy with spectral recovery using frequency domain data at a discrete number of wavelengths, as compared to that with broadband continuous wave data. Data with more wavelengths in the frequency domain always produce superior quantitative spectroscopy results with reduced noise and error in the chromophore concentrations. Performance of the algorithm in the situation of doing region-guided spectroscopy within the MRI is also considered, and the issue of false positive prior regions being identified is examined to see the effect of added wavelengths. The results indicate that broadband frequency domain data are required for maximal accuracy. A broadband frequency domain experimental system was used to validate the predictions, using a mode-locked Ti:sapphire laser for the source between 690- and 850-nm wavelengths. The 80-MHz pulsed signal is heterodyned with photomultiplier tube detection, to lower frequency for data acquisition. Tissue-phantom experiments with known hemoglobin absorption and tissue-like scatter values are used to validate the system, using measurements every 10 nm. More wavelengths clearly provide superior quantification of total hemoglobin values. The system and algorithms developed here should provide an optimal way to quantify regions with the goal of image-guided breast tissue spectroscopy within the MRI. PMID:19021313

Wang, Jia; Davis, Scott C.; Srinivasan, Subhadra; Jiang, Shudong; Pogue, Brian W.; Paulsen, Keith D.

2010-01-01

387

Comparison of advanced turboprop and conventional jet and propeller aircraft flyover noise annoyance - Preliminary results  

NASA Technical Reports Server (NTRS)

A laboratory experiment was conducted to compare the flyover noise annoyance of proposed advanced turboprop aircraft with that of conventional turboprop and jet aircraft. The effects of fundamental frequency and tone-to-broadband noise ratio on advanced turboprop annoyance were also examined. A computer synthesis system was used to generate 18 realistic, time varyring simulations of propeller aircraft takeoff noise in which the harmonic content was systematically varied to represent the factorial combinations of six fundamental frequencies ranging from 67.5 Hz to 292.5 Hz and three tone-to-broadband noise ratios of 0, 15, and 30 dB. These advanced turboprop simulations along with recordings of five conventional turboprop takeoffs and five conventional jet takeoffs were presented at D-weighted sound pressure levels of 70, 80, and 90 dB to 32 subjects in an anechoic chamber. Analyses of the subjects' annoyance judgments compare the three categories of aircraft and examine the effects of the differences in harmonic content among the advanced turboprop noises. The annoyance prediction ability of various noise measurement procedures and corrections is also examined.

Mccurdy, D. A.

1985-01-01

388

Comparison of advanced turboprop and conventional jet and propeller aircraft flyover noise annoyance: Preliminary results  

NASA Technical Reports Server (NTRS)

A laboratory experiment was conducted to compare the flyover noise annoyance of proposed advanced turboprop aircraft with that of conventional turboprop and jet aircraft. The effects of fundamental frequency and tone-to-broadband noise ratio on advanced turboprop annoyance were also examined. A computer synthesis system is used to generate 18 realistic, time varying simulations of propeller aircraft takeoff noise in which the harmonic content is systematically varied to represent the factorial combinations of six fundamental frequencies ranging from 67.5 Hz to 292.5 Hz and three tone-to-broadband noise ratios of 0, 15, and 30 dB. These advanced turboprop simulations along with recordings of five conventional turboprop takeoffs and five conventional jet takeoffs are presented at D-weighted sound pressure levels of 70, 80, and 90 dB to 32 subjects in an anechoic chamber. Analyses of the subjects' annoyance judgments compare the three categories of aircraft and examine the effects of the differences in harmonic content among the advanced turboprop noises. The annoyance prediction ability of various noise measurement procedures and corrections is also examined.

Mccurdy, D. A.

1985-01-01

389

Performance analysis of wireless broadband systems employing optical fiber links  

Microsoft Academic Search

This paper reports an analysis of the performance of wireless broadband communication systems employing fiber-optic links to connect the base station with the control station. Rainfall attenuation on the radio link, and nonlinear distortions arising from the direct modulation of the laser source, besides the noise contributions coming out from both the optical transmitter and receiver, are considered in the

Roberto Sabella

1999-01-01

390

Method and apparatus for recording broad-band seismic data  

SciTech Connect

A receiver array for detecting seismic reflections is composed of geophones of several different natural frequencies divided into subarrays having lengths compatible with the natural frequencies of their geophones and the seismic wavelengths at the recording site. This system provides both frequency and spatial filtering at the sensors so as to enhance the signal-to-noise ratio of broad-band seismic signals.

Fix, J.E.; Crews, G.A.

1985-02-12

391

ACTS broadband aeronautical terminal  

NASA Technical Reports Server (NTRS)

This paper discusses the design of, and experiments with, the ACTS Broadband Aeronautical Terminal. As part of the ongoing effort to investigate commercial applications of ACTS technologies, NASA's Jet Propulsion Laboratory and various industry/government partners are developing a broadband mobile terminal for aeronautical applications. The ACTS Broadband Aeronautical Terminal is designed to explore the use of K/Ka-band for high data rate aeronautical satellite communications. Currently available commercial aeronautical satellite communications systems are only capable of achieving data rates on the order of tens of kilobits per second. The broadband terminal used in conjunction with the ACTS mechanically steerable antenna, can achieve data rates of 384 kilobits per second, while use of an ACTS spot beam antenna with this terminal will allow up to T1 data rates (1.544 megabits per second). The aeronautical terminal will be utilized to test a variety of applications that require a high data rate communications link. The use of the K/Ka-band for wideband aeronautical communications has the advantages of spectrum availability and smaller antennas, while eliminating the one major drawback of this frequency band, rain attenuation, by flying above the clouds the majority of the time.

Agan, M. J.; Densmore, A. C.

1995-01-01

392

Independent processing across spatial frequency in moving broadband patterns.  

PubMed

The aim of the experiments was to discover whether the visual system has independent access to motion information at different spatial scales when presented with a broadband stimulus. Subjects were required to discriminate between a pair of two-frame motion sequences, one containing a coherently displacing pattern and the other containing a pattern with high-frequency noise. The stimuli were either narrowband (1 octave) or broadband (6 octaves spanning 0.23-15.0 cycles deg-1) and their power spectra were either flat or followed a 1/f2 function. For the broadband stimuli, noise was introduced cumulatively into increasingly lower frequencies. For the narrowband stimuli, noise was introduced into the same frequency band as the signal. All stimuli could be defined by the lowest noise frequency (nl) they contained. For each stimulus, the largest spatial displacement across the two frames at which the task could be performed was measured (dmax). For the narrowband stimuli, dmax increased as nl was lowered. This was true over the entire frequency range for the 1/f2 stimuli, though the task became impossible for the flat-spectrum stimuli at the lowest frequencies. This is attributed to the very low contrast of these latter stimuli. The dmax values for the broadband stimuli tended to shadow those of the narrowband stimuli with the equivalent values of nl being around 25% lower. The data were modelled by spatiotemporally filtering the stimuli and considering the amount of directional power in the signal and noise sequences. The results suggest that there must be multiple spatial-frequency channels in operation, and that for broadband patterns the visual system has perceptual access to these individual channel outputs, utilising different filters depending on the task requirements. PMID:9509157

Eagle, R A

1997-01-01

393

Supersonic Jet Exhaust Noise at High Subsonic Flight Speed  

NASA Technical Reports Server (NTRS)

An empirical model to predict the effects of flight on the noise from a supersonic transport is developed. This model is based on an analysis of the exhaust jet noise from high subsonic flights of the F-15 ACTIVE Aircraft. Acoustic comparisons previously attainable only in a wind tunnel were accomplished through the control of both flight operations and exhaust nozzle exit diameter. Independent parametric variations of both flight and exhaust jet Mach numbers at given supersonic nozzle pressure ratios enabled excellent correlations to be made for both jet broadband shock noise and jet mixing noise at flight speeds up to Mach 0.8. Shock noise correlated with flight speed and emission angle through a Doppler factor exponent of about 2.6. Mixing noise at all downstream angles was found to correlate well with a jet relative velocity exponent of about 7.3, with deviations from this behavior only at supersonic eddy convection speeds and at very high flight Mach numbers. The acoustic database from the flight test is also provided.

Norum, Thomas D.; Garber, Donald P.; Golub, Robert A.; Santa Maria, Odilyn L.; Orme, John S.

2004-01-01

394

Aeroacoustics: Fan, STOL, and boundary layer noise; sonic boom; aeroacoustic instrumentation  

Microsoft Academic Search

Fan, STOL, and boundary layer origins of aircraft noise pollution are considered, as well as certain sonic boom problems, and some means of measuring noise pollution are discussed. Topics covered include broadband noise generation by airfoils and axial flow fans, inlet geometry and axial Mach number effects on fan noise propagation, source noise suppression of subsonic tip speed fans, surface

H. T. Nagamatsu

1975-01-01

395

Electroelastic modeling and experimental validations of piezoelectric energy harvesting from broadband random vibrations of cantilevered bimorphs  

NASA Astrophysics Data System (ADS)

We present electroelastic modeling, analytical and numerical solutions, and experimental validations of piezoelectric energy harvesting from broadband random vibrations. The modeling approach employed herein is based on a distributed-parameter electroelastic formulation to ensure that the effects of higher vibration modes are included, since broadband random vibrations, such as Gaussian white noise, might excite higher vibration modes. The goal is to predict the expected value of the power output and the mean-square shunted vibration response in terms of the given power spectral density (PSD) or time history of the random vibrational input. The analytical method is based on the PSD of random base excitation and distributed-parameter frequency response functions of the coupled voltage output and shunted vibration response. The first of the two numerical solution methods employs the Fourier series representation of the base acceleration history in an ordinary differential equation solver while the second method uses an Euler-Maruyama scheme to directly solve the resulting electroelastic stochastic differential equations. The analytical and numerical simulations are compared with several experiments for a brass-reinforced PZT-5H bimorph under different random excitation levels. The simulations exhibit very good agreement with the experimental measurements for a range of resistive electrical boundary conditions and input PSD levels. It is also shown that lightly damped higher vibration modes can alter the expected power curve under broadband random excitation. Therefore, the distributed-parameter modeling and solutions presented herein can be used as a more accurate alternative to the existing single-degree-of-freedom solutions for broadband random vibration energy harvesting.

Zhao, S.; Erturk, A.

2013-01-01

396

Comparison of the Performance of Noise Metrics as Predictions of the Annoyance of Stage 2 and Stage 3 Aircraft Overflights  

NASA Technical Reports Server (NTRS)

Thirty audiometrically screened test participants judged the relative annoyance of two comparison (variable level) and thirty-four standard (fixed level) signals in an adaptive paired comparison psychoacoustic study. The signal ensemble included both FAR Part 36 Stage 2 and 3 aircraft overflights, as well as synthesized aircraft noise signatures and other non-aircraft signals. All test signals were presented for judgment as heard indoors, in the presence of continuous background noise, under free-field listening conditions in an anechoic chamber. Analyses of the performance of 30 noise metrics as predictors of these annoyance judgments confirmed that the more complex metrics were generally more accurate and precise predictors than the simpler methods. EPNL was somewhat less accurate and precise as a predictor of the annoyance judgments than a duration-adjusted variant of Zwicker's Loudness Level.

Pearsons, Karl S.; Howe, Richard R.; Sneddon, Matthew D.; Fidell, Sanford

1996-01-01

397

A 2.5-dimensional method for the prediction of structure-borne low-frequency noise from concrete rail transit bridges.  

PubMed

Predicting structure-borne noise from bridges subjected to moving trains using the three-dimensional (3D) boundary element method (BEM) is a time consuming process. This paper presents a two-and-a-half dimensional (2.5D) BEM-based procedure for simulating bridge-borne low-frequency noise with higher efficiency, yet no loss of accuracy. The two-dimensional (2D) BEM of a bridge with a constant cross section along the track direction is adopted to calculate the spatial modal acoustic transfer vectors (MATVs) of the bridge using the space-wave number transforms of its 3D modal shapes. The MATVs calculated using the 2.5D method are then validated by those computed using the 3D BEM. The bridge-borne noise is finally obtained through the MATVs and modal coordinate responses of the bridge, considering time-varying vehicle-track-bridge dynamic interaction. The presented procedure is applied to predict the sound pressure radiating from a U-shaped concrete bridge, and the computed results are compared with those obtained from field tests on Shanghai rail transit line 8. The numerical results match well with the measured results in both time and frequency domains at near-field points. Nevertheless, the computed results are smaller than the measured ones for far-field points, mainly due to the sound radiation from adjacent spans neglected in the current model. PMID:24815255

Li, Qi; Song, Xiaodong; Wu, Dingjun

2014-05-01

398

Acoustic Prediction State of the Art Assessment  

NASA Technical Reports Server (NTRS)

The acoustic assessment task for both the Subsonic Fixed Wing and the Supersonic projects under NASA s Fundamental Aeronautics Program was designed to assess the current state-of-the-art in noise prediction capability and to establish baselines for gauging future progress. The documentation of our current capabilities included quantifying the differences between predictions of noise from computer codes and measurements of noise from experimental tests. Quantifying the accuracy of both the computed and experimental results further enhanced the credibility of the assessment. This presentation gives sample results from codes representative of NASA s capabilities in aircraft noise prediction both for systems and components. These include semi-empirical, statistical, analytical, and numerical codes. System level results are shown for both aircraft and engines. Component level results are shown for a landing gear prototype, for fan broadband noise, for jet noise from a subsonic round nozzle, and for propulsion airframe aeroacoustic interactions. Additional results are shown for modeling of the acoustic behavior of duct acoustic lining and the attenuation of sound in lined ducts with flow.

Dahl, Milo D.

2007-01-01

399

Noise Radiation from Engine Cooling Fans  

NASA Astrophysics Data System (ADS)

The semi-empirical formulation previously derived by the authors (Journal of Sound and Vibration200,379-399) for predicting noise spectra of axial flow fans running in a free field is extended to engine cooling fans installed in full-size vehicles. Because of the presence of shroud, upstream radiator/condenser, and downstream engine block, the ingested and discharged flow fields around the fan blades are completely different from those in a free field. Accordingly, the noise generation mechanisms become much more difficult to analyze and model. The shroud may significantly increase the unsteady fluctuating forces exerted on the fan blades, thus greatly enhancing the levels of the discrete sounds centred at the blade passage frequency and its harmonics. The upstream radiator/condenser set may induce a significant amount of intake turbulence, thus raising the levels of the broadband sounds. The downstream engine block may force the airflow to recirculate to the front and more importantly, raise the static pressure drop across the fan assembly, which has a direct impact on the resulting flow rate. Obviously, an exact description of the effects of these factors on the resulting noise spectra is not possible. In this paper it is shown that these factors can be approximated by using certain shapes and functions. The computer model thus developed is used to predict the noise spectra from different fan assemblies under various working conditions, and the results thus obtained are compared with the measured data. Also, this model is used to calculate the overall sound pressure levels from dimensionally similar fans running under different working conditions, and the results are compared with those predicted by the fan laws currently in use by engineers in the automotive industry.

Wu, S. F.; Su, S.; Shah, H.

1998-09-01

400

Noise radiation characteristics of the Westinghouse WWG-0600 (600kW) wind turbine generator  

NASA Technical Reports Server (NTRS)

Acoustic data are presented from five different WWG-0600 machines for the wind speed range 6.7 to 13.4 m/s, for a power output range of 51 to 600 kW and for upwind, downwind and crosswind locations. Both broadband and narrowband data are presented and are compared with calculations and with similar data from other machines. Predicted broadband spectra are in good agreement with measurements at high power and underestimate them at low power. Discrete frequency rotational noise components are present in all measurements and are believed due to terrain induced wind gradients. Predictions are in general agreement with measurements upwind and downwind but underestimate them in the crosswind direction.

Shepherd, Kevin P.; Hubbard, Harvey H.

1989-01-01

First Page Previous Page 1 2 3 4 5 6 7 8